Abstract:
There are provided a mail server, a mail receiving apparatus, a mail server program storage medium, and a mail receiving program storage medium, the mail server which relays transmission and reception of electronic mail including a mail receiving section which receives electronic mail to which an attachment file is attached and which is accompanied by accompanying information which describes modes of treating the attachment file in association with plural recipient types into which recipients are categorized, an attachment file processing section which processes the attachment file of the electronic mail received at the mail receiving section in accordance with the type of recipients on the basis of the accompanying information which accompanies the electronic mail, and a mail sending section which sends the electronic mail the attachment file of which has been processed by the attachment file processing section to recipients of the electronic mail.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a mail server which relays transmission and reception of electronic mail, a mail receiving apparatus which receives electronic mail, a mail server program storage medium having stored thereon a mail server program causing a computer to function as a mail server, and mail receiving program storage medium having stored thereon a mail receiving program causing a computer to function as a mail receiving apparatus.  
         [0003]     2. Description of the Related Art  
         [0004]     With the proliferation of personal computers and remarkable improvements in communication technology, electronic mail has become popular and has been used as common information communicating means. General-purpose electronic mailing software is typically installed in personal computers and cellular phones including mail facilities. Electronic mail can be sent by using an edit screen provided by the electronic mailing software to specify a mail address in a recipient address field, specifying an attachment file, editing a mail message, and then selecting a send button. Further, electronic mail can be sent to multiple mail addresses by specifying the mail addresses in the recipient address field without the need for creating multiple copies of the same electronic mail.  
         [0005]     When electronic mail is used within a company, copies of the same electronic mail are often sent to multiple recipients. The multiple recipients may include important recipients to which an attachment file must be sent with the mail message, secondary recipients to which only the mail message needs to be sent for information purpose, and cellular phones that can receive only electronic mail of small data size at a time. If electronic mail with an attachment file is created and multiple addresses are specified in its recipient field in conventional mailing software, the electronic mail with the attachment file is sent to all mail addresses specified. However, some of the recipients may not be able to receive attachment files of large data size, or do not need the attachment file, which may consume extra time and communication charge or storage at the recipients. To solve such a problem, two pieces of electronic mail having the same message with and without the attachment file may be created and one of the two pieces of electronic mail may be sent selectively depending on recipients. However, this method has the drawback of requiring the labor of creating the two pieces of electronic mail with the same message.  
         [0006]     With regard to the problem, Japanese Patent Laid-Open No. 11-212884 describes a method in which an attachment file is selectively assigned to each of multiple types of recipient addresses (To; Cc, carbon copy; and Bcc, blind carbon copy) which are provided in typical electronic mailing software and recipient mail addresses are categorized into the multiple types, thereby sending electronic mail with the attachment file and electronic mail without the attachment file. According to that method, a user can specify whether to attach an attachment file by specifying a mail address as one of the address types, without having to creating two pieces of electronic mail having the same message.  
         [0007]     However, the approach described in Japanese Patent Laid-Open No. 11-212884 has the problem that two copies of electronic mail, one with an attachment file and the other without the attachment file, are sent from the client device generating the electronic mail to the mail server which relays transmission of electronic mail, which increases communication traffic between the mail client and the mail server.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention has been made in view of the above circumstances and provides a mail server, a mail receiving apparatus, a mail server program, and a mail receiving program that enable pieces of electronic mail to which an attachment file is attached or not attached depending on recipients to be sent without increasing communication traffic between a mail client device and a mail server.  
         [0009]     The present invention provides a mail server which relays transmission and reception of electronic mail, including: a mail receiving section which receives electronic mail to which an attachment file is attached and which is accompanied by accompanying information which describes modes of treating the attachment file in association with plural recipient types into which recipients are categorized; an attachment file processing section which processes the attachment file of the electronic mail received at the mail receiving section in accordance with the type of recipients on the basis of the accompanying information which accompanies the electronic mail; and a mail sending section which sends the electronic mail the attachment file of which has been processed by the attachment file processing section to recipients of the electronic mail.  
         [0010]     According to the mail server of the present invention, the attachment file attached to the electronic mail is processed in accordance with the types of the recipients on the basis of the accompanying information which accompanies the electronic mail and the electronic mail of which the attachment file has been processed is sent to the recipients. For example, if electronic mail is received in which information indicating whether an attachment file is to be attached or not is associated with the three recipient types, To (a primary recipient), Cc (a secondary recipient), and Bcc (a recipient to which mail addresses are not disclosed), which have been widely used and multiple recipients are categorized into the three recipient types, the electronic mail to which the attachment file is attached or the electronic mail from which the attachment file is excluded is sent according to the types of the recipients. Because electronic mail in which multiple recipient addresses are specified is sent from a mail client, the sender of the electronic mail, only once, the electronic file with and without the attachment file depending on the recipients can be sent without increasing communication traffic between the mail client device and the mail server.  
         [0011]     Preferably, in the mail server of the present invention, the accompanying information which accompanies the electronic mail received at the mail receiving section is attachment permission/prohibition information instructing whether the attachment file is to be kept attached to the electronic mail or excluded from the electronic mail in accordance with the type of recipients, and the attachment file processing section keeps the attachment file attached to the electronic mail or excludes the attachment file from the electronic mail according to the type of recipients on the basis of the attachment permission/prohibition information.  
         [0012]     Because the attachment file is attached to or excluded from the electronic mail in accordance with type of the recipients, the attachment file can be sent only to the recipient that requires the attachment file.  
         [0013]     In the mail server of the present invention, preferably the mail server according to the present invention, wherein the accompanying information which accompanies the electronic mail received at the mail receiving section is storage instructing information which instructs to exclude the attachment file from the electronic mail and to store the attachment file separately from the electronic mail, and the attachment file processing section stores the attachment file of the electronic mail and excludes the attachment file from the electronic mail to be sent to a recipient of the type associated with the storage instructing information and generates a piece of electronic mail to which the address at which the attachment file is stored is added.  
         [0014]     The mail server according to this preferable embodiment allows a recipient for whom an attachment file is excluded from electronic mail to see the attachment file by referring to its storage address attached to the electronic mail.  
         [0015]     The present invention also provides a mail receiving apparatus which receives electronic mail sent from a mail server which relays transmission and reception of electronic mail, including; a mail receiving section which receives electronic mail with information indicating whether or not an attachment file is excluded from the electronic mail; a display which displays the electronic mail received at the mail receiving section; and a display control section which, if an attachment file is excluded from the electronic file received at the mail receiving section, causes information indicating that an attachment file is excluded from the electronic mail to be displayed on the display along with the electronic mail.  
         [0016]     The mail receiving apparatus of the present invention allows a user to readily know that an attachment file is excluded from electronic mail sent from the mail server.  
         [0017]     The present invention also provides a mail server program storage medium having stored thereon a mail server program to be executed in a computer system to cause the computer system to relay transmission and reception of electronic mail, the mail server program configuring on the computer system having: a mail receiving section which receives electronic mail to which an attachment file is attached and which is accompanied by accompanying information which describes modes of treating the attachment file in association with plural recipient types into which recipients are categorized; an attachment file processing section which processes the attachment file of the electronic mail received at the mail receiving section in accordance with the type of recipients on the basis of the accompanying information which accompanies the electronic mail; and a mail sending section which sends the electronic mail the attachment file of which has been processed by the attachment file processing section to recipients of the electronic mail.  
         [0018]     The mail server program of the present invention can cause a computer to function as a mail server that can send electronic mail with or without an attachment file depending on the recipients.  
         [0019]     Any of the components such as the mail receiving section that are configured by the mail server program according to the present invention may be a single component configured by a single program component, may be a single component configured by multiple program components, or may be multiple components configured by a single program component. Also, the program itself may implement these components or may instruct another program or components thereof to implement these components.  
         [0020]     While only basic implementations of the mail server program of the present invention are described herein only to avoid overlapping, the mail server program according to the present invention is not limited to the basic implementations. Instead, various implementations that correspond to the implementations of the mail server described above are also included in the mail server program.  
         [0021]     The present invention also provides a mail receiving program storage medium having stored thereon a mail receiving program to be executed in a computer system to cause the computer system to receive electronic mail sent from a mail server which relays transmission and reception of electronic mail, the mail receiving program configuring on the computer system having: a mail receiving section which receives electronic mail with information indicating whether or not an attachment file is excluded from the electronic mail; a display which displays the electronic mail received at the mail receiving section; and a display control section which, if an attachment file is excluded from the electronic file received at the mail receiving section, causes information indicating that an attachment file is excluded from the electronic mail to be displayed on the display along with the electronic mail.  
         [0022]     The mail receiving program of the present invention can cause a computer to function as a mail receiving apparatus which allows a user to readily know that an attachment file is excluded from electronic mail sent from the mail server.  
         [0023]     Any of the components such as the mail receiving section that are configured by the mail server program according to the present invention may be a single component configured by a single program component, may be a single component configured by multiple program components, or may be multiple components configured by a single program component. Also, the program itself may implement these components or may instruct another program or components thereof to implement these components.  
         [0024]     As has been described above, the present invention can provide a mail server, a mail receiving apparatus, a mail server program storage medium, and a mail receiving program storage medium that enable pieces of electronic mail to which an attachment file is attached or not attached depending on recipients to be sent without increasing communication traffic between a mail client device and a mail server. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  schematically shows an exemplary communication system to which one embodiment of the present invention is applied;  
         [0026]      FIG. 2  is a hardware configuration of a personal computer  10 ;  
         [0027]      FIG. 3  shows functional blocks required for implementing functions unique to the embodiment on the personal computer  10 ;  
         [0028]      FIG. 4  shows an exemplary mail editing screen;  
         [0029]      FIG. 5  shows an example of edited electronic mail;  
         [0030]      FIG. 6  shows functional blocks required for implementing functions unique to the embodiment on a mal server  20 ;  
         [0031]      FIG. 7  is a flowchart of a process flow performed on the mail server  20 ;  
         [0032]      FIG. 8  shows an image of electronic mail created in an attachment file processing section  320 ;  
         [0033]      FIG. 9  is a flowchart of process flow performed on personal computers  10 A,  10 B, and  10 C; and  
         [0034]      FIG. 10  shows an exemplary electronic mail display screen. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0036]      FIG. 1  schematically shows an example of a communication system to which one embodiment of the present invention is applied.  
         [0037]     Shown in  FIG. 1  are four personal computers  10 A,  10 B,  10 C, and  10 D (hereinafter collectively referred to as PC  10 ) having an electronic mailing facility, a mail server  20  which relays electronic mail sent to the PC  10 , a Web server  30  on which various files are stored, and a communication network  40  which interconnects the PC  10 , the mail serve  20 , and the Web serve  30 . While many PC and other devices are connected to the communication network  40  in practice, only the components required for describing the present invention are shown in  FIG. 1  for simplicity.  
         [0038]     In the present embodiment, electronic mail destined to the PC  10  is received and stored at the mail server  20 . When a request for receiving the mail is sent from the PC  10  to the mail server  20 , the electronic mail received and stored on the mail server  20  is sent to the PC  10  and received by the PC  10 .  
         [0039]     In the present embodiment, the mail server  20  and the Web server  30  are workstations or a large-scale computer having a larger capacity of the memory and higher throughput of the CPU than the PC  10 ; however, their appearances and hardware configurations are similar to those of the PC  10 . In the following description, like components of the PC  10 , the mail server  20 , and the Web server  30  are labeled with like reference numerals and a configuration of the PC  10  will be described as a typical example.  
         [0040]     The PC  10 , as viewed from outside, includes a system unit  11 , a display  12  on which images are displayed in response to instructions from the system unit  11 , a keyboard  13  which inputs various types of information into the system unit  11  in response to key operations, and a mouse  14  for specifying a particular position on the display  12  to input an instruction corresponding to an icon, for example, displayed in that position.  
         [0041]      FIG. 2  shows a hardware configuration of the PC  10 .  
         [0042]     As shown in  FIG. 2 , contained in the system unit  11  are a CPU  111  which executes programs, a RAM  112  into which a program stored in a hard disk unit  121  is read and loaded for execution by the CPU  111 , the hard disk unit  121  in which programs and data are stored, a hard disk controller  113  which controls access to the hard disk unit  121 , an MO drive  114  which accesses an MO  122  loaded therein, a CD/DVD drive  115  which accesses a CD-ROM  123  or a DVD, a display controller  118 , a keyboard controller  117 , and a mouse controller  116  which control the display  12 , keyboard  13 , and mouse  14  shown in  FIG. 1 , respectively, and a communication board  119  which sends and receives a data to and from the mail server  20  and the Web server  30  shown in  FIG. 1 . These components are interconnected through a bus  110 .  
         [0043]     The mail server  20  and the Web server  30  have basically the same configuration as that of the PC  10  described above.  
         [0044]     Described below are functions of a data receiving apparatus of the present invention in the PC  10  according to one embodiment and functions of the mail server of the present invention in the mail server  20  according to one embodiment.  
         [0045]     Functions performed on the PC  10  will be described first.  
         [0046]      FIG. 3  shows functional blocks required for implementing functions unique to the present embodiment, which are formed by a combination of the hardware of the PC  10  shown in  FIG. 1  and a program executed on the CPU  111  of the PC  10 .  
         [0047]     The PC  10  has a sending function of editing and sending electronic mail and a receiving function of receiving electronic mail and displaying it on the display  12 . Shown in  FIG. 3  are a receiving section  210  including a mail receiving section  211 , a header analyzing section  212 , and a displaying section  213  and a sending unit  220  including a mail editing section  221  and a mail sending section  222 .  
         [0048]     A mail edit screen for a user to edit electronic mail is originally provided in the PC  10 .  
         [0049]      FIG. 4  shows an example of the mail edit screen.  
         [0050]     In the PC  10 , electronic-mail recipient addresses can be specified as one of three types: a TO type which represents a main recipient, a CC type which represents a secondary recipient, and a BCC type in which the address of the recipient is not notified to the TO and CC-type recipients. Provided on the mail edit screen  400  are a subject edit field  410  in which the subject of electronic mail is edited, a TO specifying field  421  in which a TO-type address is specified, a CC specifying field  422  in which a CC-type address is specified, a BCC specifying field  423  in which a BCC-type address is specified, an attachment file specifying field  430  in which an attachment file is specified, a message edit field  440  in which a mail message is edited, and attachment buttons  421   a,    422   a,  and  423   a  for specifying one of three attachment modes (mode  1 : the attachment file is attached, mode  2 : the address on the Web server  30  (see  FIG. 1 ) at which the attachment file is stored is attached, and mode  3 : neither the attachment file nor the storage address is attached) which indicate whether or not an attachment file should be sent to the recipients categorized as each of the address types.  
         [0051]     The keyboard  13  and the mouse  14  shown in  FIG. 1  act as the mail edit section  221  shown in  FIG. 3  for editing electronic mail according to information inputted by a user using the mail edit screen  400 .  
         [0052]      FIG. 5  shows an example of edited electronic mail.  
         [0053]     An electronic mail  500  includes a primary header  510  which is edited according to information specified in the subject edit field  410 , the attachment file specifying field  430 , the TO specifying field  421 , the CC specifying field  422 , and the BCC specifying field  423 , and the mail address of the PC  10 ; an extension header  520  which is edited according to information specified with the attachment buttons  421   a,    422   a,  and  423   a;  a mail message  530  which is edited according to edits made in the message edit field  440 ; and an attachment file (not shown). The extension header  520  represents an example of accompanying information as used in the present invention.  
         [0054]     Electronic mail edited in the mail editing section  221  shown in  FIG. 3  is provided to the mail sending section  222 .  
         [0055]     The mail sending section  222  sends the electronic mail edited in the mail edit section  221  to the mail server  20  through the communication board  119  shown in  FIG. 2 .  
         [0056]     The mail receiving section  211  receives electronic mail sent from the mail server  20 . The electronic mail received is provided to the header analyzing section  212 . The mail receiving section  211  represents an example of the mail receiving section in the mail receiving apparatus of the present invention.  
         [0057]     The header analyzing section  212  analyzes on the basis of the primary header  510  and the extension header  520  shown in  FIG. 5  whether or not a piece of electronic mail received at the mail receiving section  211  is one from which an attachment file is excluded. The method for analyzing this will be described in detail later. If an attachment file is excluded from the electronic mail, the header analyzing section  212  causes the displaying section  213  to display notification that an attachment file is excluded. The header analyzing section  212  represents the display control section of the mail receiving apparatus of the present invention.  
         [0058]     The display  12  and the display controller  117  shown in  FIG. 2  act as the displaying section  213 , which displays electronic mail received at the mail receiving section  211 . The displaying section  213  also displays notification that an attachment file is excluded, along with the electronic mail, if a direction to display such notification is provided from the header analyzing section  212 . The displaying section  213  represents an example of the display of the mail receiving apparatus of the present invention.  
         [0059]     Functions performed on the mail server  20  will be described below.  
         [0060]      FIG. 6  shows functional blocks required for implementing functions unique to the present embodiment, which are formed by the hardware of the mail server  20  shown in  FIG. 1  and a program executed on the CPU  111  of the mail sever  20 .  
         [0061]     Shown in  FIG. 6  are a mail receiving section  310 , an attachment file processing section  320 , a mail sending section  330 , and a mail storage  331 . The Web server  30  shown in  FIG. 1  is also shown in  FIG. 6 .  
         [0062]     The mail receiving section  310  receives electronic mail destined to the PC  10  shown in  FIG. 3 . The electronic mail received is provided to the attachment file processing section  320 . The electronic mail receiving section  310  represents one example of the mail receiving section of the mail server of the present invention.  
         [0063]     The attachment file processing section  320  obtains, from the primary header  510  and extension header  520  in electronic mail (see  FIG. 5 ) an attachment mode (mode  1 : an attachment file is attached, mode  2 : an attachment file is not attached but the address on the Web server  30  at which the attachment file is stored is attached, and mode  3 : neither of the attachment file and the address is attached) for each of the TO, CC, and BCC address types, and generates a piece of electronic mail according to each attachment mode. That is, the attachment file processing section  320  generates a piece of electronic mail to which an attachment file is attached for addresses of attachment mode  1 ; stores the attachment file in the file storage  31  on the Web server  30 , obtains the URL at which the attachment file is stored, and generates a piece of electronic mail to which the URL of the storage location is added to the mail message for addresses of attachment mode  2 ; and generates a piece of electronic mail excluding the attachment file for addresses of attachment mode  3 . The pieces of electronic mail generated are provided to the mail sending section  330 . The attachment file processing section  320  represents an example of the attachment file generating section of the mail server of the present invention.  
         [0064]     The mail sending section  330  temporarily stores electronic mail provided from the attachment file processing section  320  in the mail storage  331 . The hard disk unit  121  (see  FIG. 2 ) of the mail server, 20  acts as the mail storage  331 . When receiving a request for receiving mail from a device, such as a PC  10 , to which electronic mail is destined, the mail sending section  330  sends the electronic mail stored in the mail storage  331  to the PC  10 . The mail sending section  330  represents an example of the mail sending section of the mail server of the present invention.  
         [0065]     The PC  10  and the mail server  20  basically have the functions as described above.  
         [0066]     Processes performed on a PC  10  and the mail server  20  will be detailed below with respect to an electronic mail sending and receiving procedure in the communication system shown in  FIG. 1 .  
         [0067]     The assumption in the following description is that PC  10 D shown in  FIG. 1  sends electronic mail to each of the remaining PCs  10 A,  10 B, and  10 C as follows: it sends an electronic mail with an attachment file to PC  10 A (attachment mode  1 ), the piece of electronic mail without the attachment file but with the URL of the location on the Web server  30  at which the attachment file is stored to PC  10 B (attachment mode  2 ), and the piece of electronic mail without the attachment file and the storage URL to the PC  10 C (attachment mode  3 ).  
         [0068]     On PC  10 D to which the electronic mail is destined, a user specifies the mail address of the PC  10 A in the TO specifying field  421  as shown in  FIG. 4 , selects the “With attachment” attachment button  421   a  for the field, specifies the mail address of PC  10 B in the CC specifying field  422 , selects the “URL” attachment button- 422   a  for the field, specifies the mail address of PC  10 C in the BCC specifying field  423 , and selects the “Without attachment” button  423   a  for the field. As a result, the mail editing section  221  (see  FIG. 3 ) of PC  10 D edits electronic mail  500  by writing the mail address of PC  10 A as a TO-type recipient address in the primary header  510  and the mail address of PC  10 B as a CC-type recipient address, and the mail address of PC  10 C as a BCC-type recipient address, and describing that the attachment file is to be added to the mail to the TO-type recipient and the URL of the storage location of the attachment file is to be added to the mail to the CC-type recipient (neither the attachment file nor its storage URL is added to the mail to the BCC-type recipient). The electronic mail  500  is sent from the mail sending section  222  of PC  10 D to the mail server  20 .  
         [0069]      FIG. 7  is a flowchart of a process flow performed on the mail server  20 .  
         [0070]     The electronic mail  500  sent from PC  10 D is received at the email receiving section  310  shown in  FIG. 6  (step S 101  in  FIG. 7 ). The electronic mail  500  received is provided to the attachment file processing section  320 .  
         [0071]     The attachment file processing section  320  obtains the extension header  520  of the electronic mail  500  (step S 102  in  FIG. 7 ). It recognizes that the attachment file is to be added to the mail to the TO-type address and the URL of the storage location of the attachment file is to be added to the mail to the CC-type recipient (neither the attachment file nor its storage URL is added to the mail to the BCC-type recipient).  
         [0072]     Then, the types of the addresses written in the primary header  510  of the electronic mail  500  are sequentially obtained (step S 103  in  FIG. 7 ). The TO-type address is obtained first in this example.  
         [0073]     Because attachment mode  1  in which an attachment file is added is selected for the TO type (step S 104  in  FIG. 7 : Yes), the attachment file processing section  320  generates a piece of electronic mail according to the primary header  510 , extension header  520 , mail message  530 , and attachment file of the electronic mail  500  (step S 105  in  FIG. 7 ).  
         [0074]      FIG. 8  shows an image of electronic mail generated by the attachment file processing section  320 .  
         [0075]     For the address type in attachment mode  1 , a piece of electronic mail  501  consisting of the primary header  510 , the extension header  520 , the mail message  530 , and the attachment file  600  is generated as shown in Part (a) of  FIG. 8 . The piece of electronic mail  501  generated is provided to the electronic mail sending section  330  shown in  FIG. 6  and is temporarily stored in the mail storage  331 . When a mail send request is sent from PC  10 A, which is the TO-type recipient, the mail sending section  330  sends the piece of electronic mail  501  stored in the mail storage  331  to the PC  10 A (step S 111  in  FIG. 7 ).  
         [0076]     Then, the CC-type recipient address is obtained at step S 103  in  FIG. 7 .  
         [0077]     Because mode  2  is set for the CC-type recipient, in which the attachment file is not to be added (step S 104  in  FIG. 7 : No) but the URL of the storage location of the attachment file is to be added (step S 106  in  FIG. 7 : Yes), the attachment file processing section  320  in  FIG. 6  sends the attachment file to the Web server  30  (step S 107  in  FIG. 7 ). At the Web server  30 , the attachment file sent is stored in the file storage  31  and the storage location URL is sent to the attachment file processing section  320  (step S 108  in  FIG. 7 ). The attachment file processing section  320  adds the storage URL obtained to the mail message  530  of the electronic mail  500  shown in  FIG. 5  (step S 109  in  FIG. 7 ).  
         [0078]     For the attachment mode  2  recipient, a piece of electronic mail  502  is generated in which the primary header  510 , the extension header, and the mail message  530  are written and the URL  600 ′, of the storage location of the attachment file is written as shown in Part (b) of  FIG. 8 . The piece of electronic mail  502  is also provided to the mail sending section  330  and, when a mail-send request is sent from PC  10 B, which is the recipient of the CC-type mail, it is sent to PC  10 B (step  111  in  FIG. 7 ).  
         [0079]     Finally, the BCC-type recipient address is obtained at step S 103  in  FIG. 7 .  
         [0080]     Because attachment mode  3  is set for the BCC-type recipient in which neither the attachment file nor the storage URL is added (steps S 104  and S 106  in  FIG. 7 : No), the attachment file processing section  320  shown in  FIG. 6  generates a piece of electronic mail excluding the attachment file (step S 110  in  FIG. 7 ).  
         [0081]     For the recipient type for which mode  3  is set, a piece of electronic mail  503  is generated in which only the primary header  510 , the extension header  520 , and the mail message  530  are contained as shown in Part (c) of  FIG. 8 . The piece of electronic mail  503  is also provided to the mail sending section  330  and, when a mail-send request is sent from PC  10 C, which is the recipient of the BCC-type mail, it is sent to PC  10 C (step S 111  in  FIG. 7 ).  
         [0082]     The following process is performed at the mail server  20 .  
         [0083]      FIG. 9  is a flowchart of a process flow performed on PCs  10 A,  10 B, and  10 C.  
         [0084]     To receive electronic mail at any of PCs  10 A,  10 B, and  10 C, its mail receiving section  211  shown in  FIG. 3  sends a receive request to the mail server  20  and the mail sending section  330  sends a piece of electronic mail  501 ,  502 , and  503  destined to the PC 10 A,  10 B,  10 C. The piece of electronic mail sent is received at the mail receiving section  211  shown in  FIG. 3  (step S 201  in  FIG. 9 ) and provided to the header analyzing section  212 .  
         [0085]     The header analyzing section  212  obtains the extension header  520  of the electronic mail and the recipient type of the PC which is written in the primary header  510  (steps  202  and  203  in  FIG. 9 ).  
         [0086]     In this example, the header analyzing section  212  obtains the extension header  520  indicating that the attachment is to be attached to the mail to the TO-type recipient and its storage URL is to be added to the mail to the CC-type recipient (neither the attachment file nor the storage URL is to be added to the mail to the BCC-type). For example, at PC  10 A, the TO type is obtained as its recipient type and accordingly it is determined that an attachment file is attached to the piece of electronic mail  501  (see Part (a) of  FIG. 8 ) sent to PC  10 A (step S 204  in  FIG. 9 : No). Consequently, only the piece of electronic mail  501  is displayed on the displaying section  213  of PC  10 A (step S 206  in  FIG. 9 ).  
         [0087]      FIG. 10  shows an exemplary electronic mail display screen.  
         [0088]     As shown in Part (a) of  FIG. 10 , a mail screen  610  including a header  611  based on the primary header  510  of the electronic mail  501 , and an attachment file name  612  based on the attachment file  600 , and a message  613  based on the message  530  are displayed on PC  10 A.  
         [0089]     On PC  10 B, it is determined that an attachment file is excluded from the electronic mail  502  sent to PC  10 B because the CC type is obtained as its recipient type (step S 204  in  FIG. 9 : Yes). The header analyzing section  212  provides an instruction to the displaying section  213  to display notification that an attachment file is excluded.  
         [0090]     The displaying section  213  of PC  10 B displays a mail screen  620  including a header  621  based on the primary header  510  of the electronic mail  502 , a send-to URL  622   a  based on the send-to URL  600 ′, a message  622  based on the message  530 , and the notification  623  that an attachment file is excluded as shown in Part (b) of  FIG. 10 . A user of PC  10 B can see the attachment file by specifying the send-to URL  622   a  with a mouse  14 B or the like.  
         [0091]     On PC  10 C, The BCC-type is obtained as its recipient type and accordingly it is determined that an attachment file is excluded from the electronic mail  503  (step S 204  in  FIG. 9 : Yes).  
         [0092]     The displaying section  213  of the PC  10 C, a screen  630  including a header  631  based on the primary header  510  of the electronic mail  503 , a message  632  based on the message  530 , and a notification  633  that an attachment file is excluded, as shown in Part (c) of  FIG. 10 . A user of PC  10 C can know from the attachment file exclusion notification  633  that a file attached to the electronic mail  503  is excluded.  
         [0093]     As has been described, the present embodiment reduces communication traffic between a mail client device (PC  10 D) that sends electronic mail and the mail server  20 , and allows electronic mail to be sent with or without an attachment file depending on recipients.  
         [0094]     While the mail server in the example described above temporarily stores electronic mail destined to PCs at the mail server sent to the PCs in response to a receive request from the PCs, the mail server of the present invention may send electronic mail to another mail server without storing it.  
         [0095]     While the mail server in the example described above relays electronic mail destined to PCs, the mail server of the present invention may relay electronic mail destined to cellular phones.  
         [0096]     While an example has been described in which electronic mail to which an extension header that associates the types of recipients with modes of treating an attachment file is received at the mail server, the association between the types of recipients and modes of treating an attachment file may be pre-established between a mail client device and the mail server and the mail server of the present invention may receive electronic mail to which only the primary header is attached. In that case, the recipient type itself written in the primary header represents accompanying information as used in the present invention.