Abstract:
System enabling the cancellation of previously-sent e-mail comprising a data transmission network, wherein a plurality of users are connected to the network, each user being able as a sender to forward an e-mail over the network to at least another user as a recipient connected to the network, and wherein a message transfer agent MTA is associated with each user for sending the e-mail when the user acts as a sender and delivering the e-mail when the user acts as a recipient. Each MTA includes a cancel mailbox for transmitting a cancellation message to the recipient(s) when the user associated with the MTA is a sender wanting to cancel a previously-sent e-mail or for managing the cancellation of e-mails in the mailbox of the user associated with the MTA upon receiving the cancellation message from the sender when this user is a recipient.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to communications by electronic mail (e-mail) through a data transmission network, and relates in particular to a method and system for canceling an e-mail message which has previously been sent to one or more recipients. 
     BACKGROUND OF THE INVENTION 
     Electronic mail (e-mail) provides a quick and convenient way for Internet users throughout the world to communicate between one another. Such a communication is initiated by a message sender composing a message, which optionally includes joined files, and addressing the message to one or more recipients. 
     Once a message has been composed and a “send” key has been activated, the message will be delivered to each of the addressed recipients automatically, provided that valid e-mail destination addresses have been used in the message. A message may pass through a number of separate server computers, generally SMTP servers (also called Message Transfer Agents (MTA)), before reaching its final destination. The action of each MTA is defined as a “store and forward” which means that each message is temporarily stored and then forwarded when the MTA has an appropriate channel available. 
     One characteristic of the Internet network is that once a message is submitted to the Internet, the message becomes an independent entity (no longer under the control of the sender). This means that, once the message has been transmitted over the Internet, it cannot be directly altered, canceled or retracting by the originating sender. 
     However, in some situations, an e-mail user can use an unsend operation. Assuming that the sender sent the message to a wrong recipient or forgot to include an important item in the message, the sender may wish to stop transmission of the message before the message reaches the recipient. In certain software packages, this operation is possible by pressing an “undo” key. However, there is a difficulty with the “undo” function for e-mail insofar as the operation usually involves a number of independent servers not under the control of the user software. 
     Some e-mail systems provide a central repository for e-mail. Using this type of e-mail system, the message sender composes the message and sends the message to the recipient. The e-mail system saves the message in the e-mail repository until the recipient retrieves the message. In such a system, the sender can stop delivery of the message if the recipient has not yet retrieved the message because the message remains within the scope of control of the originating e-mail system. 
     Another messaging scheme is the Usenet Network News facility (netnews) that is well known to the art. Netnews has a “cancel” feature that allows the author of a message to send a follow-up cancel message that causes the recipient computers to remove the original message from their news directory. This netnews feature relies on the standardized nature of netnews—all recipient computers are programmed to process cancel messages. 
     However, in the above systems, once an e-mail has passed beyond the control of the originating sender, the e-mail cannot be canceled. This problem has been solved in systems wherein a cancel message is sent by the sender to all the recipients of the first message. Such a cancel message is either a duplicate message of the original message including a canceling tag or an action message including some information contained in the original message. Once this second message is received by the recipient, both original message and cancel message are deleted if the original message has not been read by the recipient. 
     Unfortunately, the above mechanism relates only to means for canceling messages which have not yet been read without looking for whether some recipients have already read the message. This means that some recipients, among the recipients who have received the e-mail, will be able to make some decisions whereas other recipients will not be able to make decisions since they will not have received the e-mail, which results in a possible discrepancy. Such a solution is not acceptable in some cases wherein an action must be achieved by all the recipients or by none of them. Therefore, there is a need to have a mechanism enabling a user to send an e-mail to each designated recipient or, conversely, to cancel this e-mail for all recipients. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention provides a method and system enabling canceling of an e-mail forwarded by a sender to one or more recipients only when none of these recipients has read the e-mail. 
     The invention relates therefore to a system enabling the cancellation of a previously-sent e-mail comprising a data transmission network (e.g., the Internet network) wherein a plurality of users are connected to the network, each user being able as a sender to send an e-mail over the network to at least another user as a recipient connected to the network, and wherein a message transfer agent (MTA) is associated with each user for sending the e-mail when the user acts as a sender and delivering the e-mail when the user acts as a recipient. Each MTA includes a cancel mailbox for transmitting a cancellation message to the recipient(s) when the user associated with the MTA is a sender wanting to cancel a previously-sent e-mail or for managing the cancellation of e-mails in the mailbox of the user associated with the MTA upon receiving a cancellation message from the sender when this user is a recipient. 
     According to another aspect of the present invention, the method of canceling a previously-sent e-mail comprises:
         sending from the sender a message for deleting the e-mail to a cancel mailbox included in the MTA,   sending from the cancel mailbox included in the sender MTA a message to a cancel mailbox included in each MTA respectively associated with each recipient being addressed in the e-mail in order to inform them that the e-mail has to be deleted if it has not yet been read,   sending from the cancel mailboxes of the MTAs respectively associated with the recipients a message requesting that the e-mail has to be masked only if it has not yet been read, and   deleting or not deleting the masked e-mail according to whether none of the recipients has read the e-mail or not.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the invention will be better understood by reading the following more particular description of the invention in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a first embodiment of a data transmission system enabling the cancellation of a previously-sent e-mail message according to the invention; 
         FIG. 2  is a time diagram of the messages which are exchanged for canceling a previously-sent e-mail in the system illustrated in  FIG. 1  when the e-mail has not yet been read; 
         FIG. 3  is a time diagram of the messages which are exchanged for the cancellation of a previously-sent e-mail in the system illustrated in  FIG. 1  when the e-mail has already been read by a recipient; 
         FIG. 4  is a second embodiment of a data transmission system enabling the cancellation of previously-sent e-mail message according to the invention; 
         FIG. 5  is a time diagram of the messages which are exchanged between the cancel mailboxes for the cancellation of a previously-sent e-mail in the system illustrated in  FIG. 4  when the e-mail has not yet been read; 
         FIG. 6  is a time diagram of the messages which are exchanged between the cancel mailboxes for the cancellation of a previously-sent e-mail in the system illustrated in  FIG. 4  when the e-mail has already been read by a recipient; 
         FIG. 7  is a schematic representation of the tables being used in a MTA device for the implementation of the method according to the invention; 
         FIG. 8  is a flowchart of the steps which are achieved for building the MTA tables illustrated in  FIG. 7 ; 
         FIG. 9  is a flowchart of the steps which are achieved in a sender MTA upon receiving a cancellation e-mail; 
         FIG. 10  is a flowchart of the steps which are achieved in an intermediate or deliver MTA upon receiving a cancellation message; and 
         FIG. 11  is a flowchart of the steps which are achieved in any MTA for performing the method of cancellation of an e-mail according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In reference to  FIG. 1 , a user  10  called the sender wants to send an e-mail or several e-mails through the Internet network  12  to several other users called the recipients such as users  14 ,  16  and  18 . It is of no importance if there is a primary recipient and that the other recipients are copied. 
     For each user, there is a server SMTP or Mail Transfer Agent (MTA) which is responsible to issue the messages from a mailbox or to deliver the messages in a mailbox. Thus, for user  10 , it is MTA  20  which receives the e-mails from user  10  and which is in charge of sending emails to the recipients. Assuming that MTA  22  is associated with the domain A including the addresses of user A 1   14  and user A 2   16 , the e-mails are sent from MTA  20  to MTA  22  which delivers the messages in the mailbox of user  14  and the mailbox of user  16 . Likewise, if it is another MTA  24  which is in charge of the address of user B  18 , the e-mails are forwarded from MTA  20  to MTA  24  which delivers the message in the mailbox of user B  18 . 
     It is assumed now that the sender  10  wants to cancel one of its previously-sent e-mails. The sender  10  issues a cancellation message containing the message to be canceled. According to the principles of the invention, the cancellation message is received by a cancel mailbox associated with MTA  20 . This cancel mailbox of the sender is responsible to manage the process of cancellation via a flow of actions described in the following and using a cancel mailbox  28  associated with MTA  22  and a cancel mailbox  30  associated with MTA  24 . 
     As illustrated in  FIG. 2 , the sender sends a cancellation message DELETE to the cancel mailbox of the sender. Upon receiving this message, the cancel mailbox of the sender forwards a message DELETE-MAIL to the cancel mailbox of MTA A and also to the cancel mailbox of MTA B. Upon receiving this message, the cancel mailbox A sends a message SUSPEND to the mailbox of each recipient A 1  and A 2 . Likewise, upon receiving the message DELETE-MAIL, the cancel mailbox B sends a message SUSPEND to the mailbox of the recipient B. 
     Assuming that the e-mail previously sent by the sender has not been read by any one of the recipients, each mailbox sends back a message SUSPEND-OK to the associated cancel mailbox as illustrated in  FIG. 2 , meaning that the message which has not yet been read will not be supplied to the recipient. 
     Upon receiving the message SUSPEND-OK from the recipient mailbox, the cancel mailbox forwards immediately a message DELETE-PENDING to the cancel mailbox of the sender, meaning that the deletion of the initial e-mail is pending. 
     Assuming that the cancel mailbox of the sender receives a message DELETE-PENDING from all the cancel mailboxes, it knows that the e-mail has not been read by any one of the recipients and that it may be deleted. Accordingly, the cancel mailbox of the sender forwards a message DELETE-COMMIT to all the cancel mailboxes. Upon receiving the message, each cancel mailbox delivers a message SUPPRESS to the mailbox of the associated recipients, that is recipients A 1  AND A 2  for cancel mailbox A and recipient B for cancel mailbox B, meaning that the e-mail must be deleted. At the same time, the cancel mailbox of the sender sends an acknowledgment message DELETE-OK to the sender in order to keep the latter aware that the message has been deleted for all recipients. 
     In a second situation illustrated in  FIG. 3 , the e-mail previously sent by the sender has already been read by one of the recipients. It is assumed that it is recipient A 2  which has already read the previously-sent e-mail. In such a case, the mailbox of recipient A 2  sends back a message SUSPEND-KO to the cancel mailbox A upon receiving the message SUSPEND from the cancel mailbox A meaning that it is not possible to suspend reading of the e-mail. Upon receiving the message, the cancel mailbox A sends a message DELETE-FAILED to the cancel mailbox of the sender. Accordingly, the cancel mailbox of the sender has received messages from all the cancel mailboxes associated to the recipients. However, at least one of these messages is a message DELETE-FAILED and not a message DELETE PENDING as for all the other cancel mailboxes. Then, the sender cancel mailbox sends back an acknowledgment message DELETE-KO to the sender mailbox meaning that the e-mail will not be deleted since at least one recipient has already read the e-mail. At the same time, the cancel mailbox of the sender forwards a message DELETE-ROLLBACK to all the cancel mailboxes associated with the recipients to inform them that they have to cancel the suspended deletion. Upon receiving the message DELETE-ROLLBACK, the cancel mailbox delivers a message ACTIVATE to the mailbox of each recipient who has not yet read the e-mail, such a message being useless for a recipient having read the e-mail. 
     In reference to  FIG. 4 , another case is when there is an intermediary MTA between the MTA associated with the sender and the MTAs associated with the recipients. Such an intermediary MTA exists when it is responsible for a specific domain name or for a distribution list. In such a case, the e-mail is first sent from MTA  20  associated with the sender  10  to the intermediary MTA  32 . The intermediary MTA  32  is then in charge of forwarding the e-mail to each MTA associated with the recipients of the e-mail, that is MTA  22  for the recipients  14  and  16  and MTA  24  for the recipient  18 . As for the other MTAs, the intermediary MTA  32  Includes a cancel mailbox  34  responsible for managing the process of cancellation. It must be noted that, in a more complex situation, it would be possible to have more than one intermediary MTA, all the intermediary MTAs constituting a hierarchy of MTAs associated with sub-domains included each in larger domain and so on. 
     As illustrated in  FIG. 5 , the cancel mailbox of the sender sends a message DELETE-MAIL to the cancel mailbox of the intermediate MTA. However, instead of delivering a message SUSPEND directly to the recipients as it was the case in reference to  FIGS. 2 and 3 , the intermediate cancel mailbox sends also a message DELETE-MAIL to cancel mailboxes A and B. The message DELETE-MAIL would be forwarded again to a subsequent intermediate cancel mailboxes if there were a hierarchy of MTAs. If the e-mail has not yet been read by any recipient, the cancel mailboxes associated with the recipients forward back a message DELETE-PENDING to the intermediate cancel mailbox which also returns a message DELETE-PENDING to the cancel mailbox of the sender. Upon receiving this message or several messages DELETE-PENDING if there are several intermediate MTAs, the cancel mailbox of the sender forwards a message DELETE-COMMIT to the intermediate cancel mailbox(es), such a message being forwarded again by all the intermediate mailboxes of the hierarchy to the cancel mailboxes responsible to deliver a message SUPPRESS to the mailboxes of the recipients. The remaining steps of this process are identical to the steps described previously in reference to  FIG. 2 . 
     Assuming that one of the recipients has already read the e-mail, the message which is returned by the cancel mailbox as illustrated in  FIG. 6  is not DELETE-PENDING but DELETE FAILED as already explained in reference to  FIG. 3 . The same message is transferred from the intermediate cancel mailbox to the cancel mailbox of the sender. As detailed previously, a message DELETE-ROLLBACK is sent from the cancel mailbox of the sender to the intermediate cancel mailbox (and to all the intermediate cancel mailboxes, if any), and finally to the cancel mailbox B responsible for activating the e-mail in the mailboxes of the other recipients, since the e-mail will not be deleted inasmuch as one of the recipients has already read it. 
     It must be noted that an intermediate MTA repeats, in both directions, any message received from the cancel mailbox of a MTA toward another MTA such as the deliver MTA in one direction or such as the sender MTA in the other direction. 
     A cancellation agent is associated with each cancel mailbox. A cancellation agent is a program in charge of reading the messages from the user mailboxes located in the associated domain to check whether a message is not yet read. The actions of the cancellation agent in the mailbox are the following:
         “Identifying an unread e-mail” in response to the message DELETE-MAIL,   “Mask an unread e-mail” before sending the message DELETE-PENDING,   “Unmask an unread message” after receiving the message DELETE-ROLLBACK”,   “Delete an e-mail” after receiving the message DELETE-COMMIT.       

     When a message  40  issued either by a user agent (UA) in case of DELETE or by a mail transfer agent (MTA) in case of DELETE-MAIL, is received by a MTA, the cancellation agent of the MTA builds a set of tables as illustrated in  FIG. 7 . First, it parses the recipient addresses received with the e-mail in order to build a Recipient table  42 . Such a table includes for each addressed recipient the MTA with which the recipient is associated. If the address corresponds to a distribution list, this distribution list is expanded. If an alias is found, the alias is replaced by the address of the aliased user. 
     Then, the Recipient table (corresponding to SDLST in  FIG. 7 ) is scanned to build a Delete Process Table  44  for each e-mail to be deleted wherein each entry corresponds to the name of the recipient. For each entry, two fields are defined in the table, the type that is UA (for User agent) or MTA, and the status corresponding to the entry. As described in the following, this field is modified according to which kind of message is received by the UA or the MTA. 
     Finally, both the Delete Process table  44  and the Recipient table  42  are mapped in a Mail Delete table  46  which is unique for each MTA. Assuming that, for an e-mail identified by XX, a Recipient table SDLST and a Delete Process table DPT have been built, the Mail Delete table  46  will include for the entry XX, SDLST pointing to the identified Recipient table and DPT pointing to the identified Delete Process table. 
     It must be noted that some MTAs can use aliases to mask their current mail infrastructure. Thus, an e-mail could be sent to john@ibm.com whereas the final address after converting the alias address is in fact john@lagaude33.ibm.com. In some cases, a domain name is managed by a MTA forwarding incoming messages for the domain. In all these cases, the problem is solved by the intermediate cancel mailbox responsible of the domain wherein the cancellation agent has access to the Domain Name Server (DNS). 
     The process achieved in cancel mailbox for canceling an e-mail received by the MTA depends on whether this MTA is the sender MTA, an intermediate MTA or the deliver MTA. For all MTAs, there is a first state, STATE  1 , as illustrated in  FIG. 8 . At the beginning, the cancel mailbox of the MTA receives a message DELETE or DELETE-MAIL (step  50 ). As described in reference to  FIG. 7 , the cancellation agent creates a recipient table SDLST (step  52 ). As there can be several recipients, a loop of steps is achieved. At the beginning, it is determined whether there is still a recipient to process (step  54 ). If so, it is determined whether the recipient name is an alias (step  56 ). If it is not the case, it is determined whether the received address corresponds to a distribution list (step  58 ). If so, it is determined whether there is another element to process in the distribution list (step  60 ) and if so, this element is added in the table SDLST (step  62 ) before checking again whether there is any more element in the distribution list. 
     When the recipient name is an alias, the aliased address is added in the table (step  64 ) and when the address does not correspond to a distribution list, the address is added in the table SDLST (step  66 ). In both cases and after all the elements of a distribution list have been added in the table, the process is looped back to the beginning for determining whether there is another recipient (step  54 ). 
     If there are no more recipients in the address list of the e-mail, the delete process table is created by the cancellation agent as described above (step  68 ). Such a creation being a loop of steps as long as there is still an element to be put in the table, it is first determined whether there is a new element for the delete process table (step  70 ). If it is the case, the process is different according to whether the MTA associated with the recipient address is a User agent (UA) or not (step  72 ). If it is an UA, this means that the recipient is under the control of this UA and a message SUSPEND is sent from the cancel mailbox of the UA to the mailbox of the recipient (step  74 ). If it is not the case, the cancel mailbox sends a message DELETE-MAIL to the MTA associated with the recipient (step  76 ). After the transmission of the message SUSPEND or DELETE-MAIL, the process is looped back to the determination of a new element for the delete process table (step  70 ). Note that, if there is no new element to be processed in the delete process table, a timer T 1  is set (step  78 ) and the process goes to STATE  2 . 
     STATE  2  is different according to whether the MTA is the sender MTA or another MTA such as an intermediate MTA or the deliver MTA. If it is the sender MTA, the process achieved in STATE  2  is illustrated by the flow chart of  FIG. 9 . At the beginning, the process is waiting for an event (step  80 ). When such an event is detected, it is determined whether it corresponds to the time out of Time 1 (step  82 ). If it is not the case, it is determined whether the event corresponds to a message SUSPEND OK sent directly from the recipient mailbox or a message DELETE-PENDING sent from a MTA (step  84 ). If it is the case, the delete process table is updated by writing the message in the status field of the entry corresponding to the recipient address (step  86 ). After that, it is determined whether the answers corresponding to all the recipients have been received (step  88 ). If not, the process is looped back to the step of waiting for an event (step  80 ). 
     When all answers from the recipient mailboxes have been received, the cancellation agent forwards a message SUPPRESS to the recipient mailbox or a message DELETE-COMMIT to the MTA (step  90 ) and at the same time sends a message DELETE-OK to the sender (step  92 ). However, when the event being received is the time out from timer T 1  or the message is not SUSPEND-OK or DELETE-PENDING, this means that the e-mail has already been read, the received message being SUSPEND-KO or DELETE-FAILED. In such a case, the cancel mailbox forwards a message ACTIVATE to the recipient mailbox or a message DELETE-ROLLBACK to the MTA (step  94 ). At the same time, it sends a message DELETE-KO to the sender to inform it that the e-mail will not be deleted because one of the recipients has already read the e-mail. In all cases, after sending the message, the process leaves STATE  2  for coming back to STATE  1 . 
       FIG. 10  illustrates STATE  2  when the MTA is an intermediate MTA or deliver MTA. At the beginning, the process is waiting for an event (step  100 ). When such an event is detected, it is determined whether it corresponds to the time out of timer T 1  (step  102 ). If it is not the case, it is determined whether the event corresponds to a message SUSPEND OK sent directly from the recipient mailbox or a message DELETE-PENDING sent from a MTA (step  104 ). If it is the case, the delete process table is updated by writing the message in the status field of the entry corresponding to the recipient address (step  106 ). After that, it is determined whether the answers corresponding to all the recipients have been received (step  108 ). If not, the process is looped back to the step of waiting for an event (step  100 ). 
     When all answers from the recipient have been received, the MTA forwards a message DELETE-PENDING to the preceding intermediate MTA or the sender MTA (step  110 ). However, when the event received is the time out of Timer T 1  or the message is not SUSPEND-OK or DELETE-PENDING, this means that the e-mail has already been read, the message being SUSPEND-KO or DELETE-FAILED. In such a case, the cancel mailbox forwards a message DELETE-FAILED to the preceding intermediate MTA or the sender MTA (step  112 ) and a Timer T 2  is set (step  114 ). In all cases, after sending the message, the process leaves STATE  2  for inputting a STATE  3 . 
     STATE  3  illustrated in  FIG. 11  starts with a step of waiting for an event (step  116 ). It is first determined whether the event is the time out of timer T 2 . If it is not the case, it is determined whether the message which has been received is DELETE-COMMIT (step  120 ) meaning that the e-mail has not been read by any one of the recipients. If so, it is necessary to know the recipients who are addressed in the e-mail. Therefore, a loop is started by determining whether there is still an element to be checked in the delete process table (step  122 ). If it is the case, it is determined whether this element (a recipient name) corresponds to a user agent (step  124 ). If so, this means that the MTA is a deliver MTA and it has to send a message SUPPRESS to the recipient mailbox in order to delete the e-mail (step  126 ). If it is not an UA, it is an intermediate MTA and the cancellation agent of the MTA has to send a message DELETE-COMMIT to the following MTA which can be an intermediate MTA or the deliver MTA (step  128 ). After sending a message SUPPRESS or DELETE-COMMIT, the process is looped back to the step of checking the next element in the delete process table (step  122 ). 
     When the event is the time out of timer T 2  or is not a message DELETE-COMMIT, this means that the e-mail has already been read by at least one of the recipients. It is therefore necessary to know the recipients in order to inform them that the e-mail will not be deleted. As detailed previously, a loop is started by determining whether there is an element to be checked in the delete process table (step  130 ). If it is the case, it is determined whether the element (a recipient name) corresponds to a user agent (step  132 ). If so, this means that the MTA is a deliver MTA and it has to send a message ACTIVATE to the recipient mailbox meaning that the e-mail may be read by the recipient (step  134 ). If it is not an UA, it is an intermediate MTA and the cancellation agent of the MTA sends a message DELETE-ROLLBACK to the following MTA which can be an intermediate MTA or the deliver MTA (step  136 ). After sending a message ACTIVATE or DELETE-ROLLBACK, the process is looped back to the step of checking the next element in the delete process table (step  130 ). Note that, if there are no more elements to be checked in the delete process table either when the event is the time out of timer T 2  or in any case upon reception of a message, STATE  3  is completed and the process goes again to STATE  1 .