Abstract:
The Secure Anti-Spam Email Protocol (SASEP) as proposed by this invention is based on public/private/invitation email address architecture. Each user that will register at any SASEP server will receive a public and a private email address. The public email address (e.g. user@domain.com) can be used as a regular email address or alias. The private email address (e.g. privatecode.user@domain.com) has to be in Bcc: field of all outgoing email messages. The user can also request arbitrary number of invitation email addresses (e.g. invitationcode.user@domain.com) that can be used for registration on web sites. The main advantage of SASEP is that the user can continue to use standard outgoing (SMTP) and incoming (POP3, IMAP or HTTP) email server and standard desktop or web email client. This is ensured by SASEP that defines an automatic mechanism for managing different lists and challenge system.

Description:
Spam can be defined as the use of any electronic communication to send unsolicited commercial or non-commercial messages in bulk and refers to different media such as email, messaging, newsgroups, mobile phones and Internet telephony. There is a number of anti-Spam technologies proposed against Spam. However, each year the volume of Spam increases. 
   The major problem of the proposed solutions is, that, they either require that most of the Internet infrastructure needs to be changed, or that they oversee an important aspect that leaves space for continuing the operation of Spam. The example for the first case is a proposal of a challenge system that requires new email servers or new email clients. The example for the second case is a proposal of a whitelist approach that oversees a possibility that everybody can find out e.g. that the email address of the second author of some published paper is probably on a whitelist of the email address of the first author. The major problem with the filtering approach is that none can guarantee that the email from some sender we have already written before, or from some site we are registered at, will not be blocked. At the same time we have Spam email messages that are not interrupted at all by a filter. 
   BRIEF SUMMARY OF THE INVENTION 
   The Secure Anti-Spam Email Protocol (SASEP) as proposed by this invention can be implemented on some separate server accessible by the already available Internet infrastructure. The user can continue to use standard outgoing (SMTP) and incoming (POP3, IMAP or HTTP) email server and standard desktop or web email client. Two isolated efforts required by SASEP providing this are that the private email address has to be in Bcc: field of all outgoing email messages and that for registration on web sites invitation email addresses have to be used. Each user being registered at some SASEP server will receive public (e.g. user@domain.com) and private (e.g. privatecode.user@domain.com) email address as well as requested number of invitation email addresses (e.g. invitationcode1.user@domain.com, invitationcode2.user@domain.com, . . . ). The rest is ensured by the SASEP server that implements automatic mechanism for managing different lists and challenge system. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  shows one possible configuration with two SASEP servers, three users, and one web site. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A system for secure communication with a solution to the Spam problem, named the Secure Anti-Spam Email Protocol (SASEP), operates according to the following. The first step is, the user with standard desktop or web email client, standard outgoing email (SMTP) server and standard incoming email (POP3, IMAP or HTTP) server, registers on SASEP server. In the second one, SASEP server provides to the user the public email address (e.g. user@domain.com) and the private email address (e.g. privatecode.user@domain.com). After that, the user can use the public email address as a regular email address or alias, while the private email address has to be in Bcc: field of all outgoing email messages. When the user wants to register on some web site, she/he requests from SASEP server the invitation email address (e.g. invitationcode.user@domain.com) for registration. It should be noted that the user can request from SASEP server a new private email address and an additional invitation email addresses at any time. 
   One possible configuration with two SASEP servers, three users, and one web site is shown in  FIG. 1 . Additionally, examples of possible email messages are given. The first user (user1) does not use SASEP, while the second (user2) and third (user3) one use SASEP. In the first case user1@domain1.com sends an email to user2@domain2.com. In the second case user2@domain2.com sends an email to user1@domain1.com wherein privatecode.user2@domain2.com is in Bcc: field. In the third case user2@domain2.com sends an email to user3@domain3.com wherein privatecode.user2@domain2.com is again in Bcc: field. And in the forth case someaddress@somesite.com sends an email to invitationcode.user3@domain3.com. It should be noted that SASEP servers could be on the same domain as the users that use them are. It should also be noted that both users could use the same SASEP server. 
   The SASEP server for each user uses internally several lists. The list containing the unique message identifiers of email messages sent by a user, is named messagelist. Using this list, SASEP server is able to confirm to other SASEP server that the user did indeed send some email. The list containing email addresses of senders authorized to send email to the user wherein senders use SASEP, is named saseplist. The list containing email addresses of senders authorized to send email to the user wherein senders use only SMTP, is named smtplist. The list containing email addresses of senders authorized to send email to the user wherein senders that use only SMTP are compromised by at least one Spam email message where the faked email address from From: field is their email address, is named compromisedlist. The list containing email addresses of senders whose email messages will be blocked, is named blacklist. And at the end, the list containing local aliases to the public email address, is named invitationlist. 
   For each email message received on invitation email address, SASEP server&#39;s responsibility is to accept received email. 
   For each email message received on private email address, SASEP server has following responsibilities. When private email address is in Bcc: field, two things should be done. Firstly, the unique message id generated by SMTP server needs to be added to the messagelist. Secondly, email addresses of all recipients that are not already on any list needs to be added to the smtplist. When private email address is in To: field and word Spam in Subject: field, the following needs to be done. If sender of forwarded email is on the smtplist, it is necessary to move its email address to the compromisedlist. Otherwise, if sender of forwarded email is not on any list, it is necessary to add its email address to the blacklist. When private email address is in To: field, it is necessary to process other commands sent by the user in Subject: field as well. Those commands can be defined as SASEP extension. 
   For each email message received on public email address, SASEP server has following responsibilities. When the sender is on saseplist, it is necessary to perform a check if this sender did send received email and if so to accept it, otherwise to delete it. When the sender that can be moved to saseplist is on smtplist or compromisedlist, it is necessary to move the sender&#39;s email address to saseplist and it is necessary to process received email in the same way as in previous case. When the sender that cannot be moved to saseplist is on the smtplist, it is necessary to accept received email. The option for SASEP server is to add warning to the text from Subject: field or to perform some other action if required by the user. When the sender that cannot be moved to saseplist is on the compromisedlist, it is necessary to send automatic response to sender requesting confirmation that the sender sent received email that is required for its acceptance. The option for SASEP server is to perform some other action if required by the user. When the sender is on the blacklist, it is necessary to delete received email. Finally, when the sender is not on any list, it is necessary to send automatic response with challenge to sender requesting results to accept received email. The option for SASEP server is as well to perform some other action if required by the user. 
   In case the sender is on saseplist, the check can be performed, if this sender did send received email as follows. First, user&#39;s SASEP server (e.g. sasep1.userdomain.com) tries to establish communication with sender&#39;s SASEP server (e.g. sasep1.senderdomain.com), using unique message id of received email and unique authorization id generated by user&#39;s SASEP server as arguments. If positive response is received within predefined time, sender&#39;s SASEP server is informed that received email was accepted. Otherwise, the email is deleted while sender&#39;s SASEP server&#39;s responsibility is to inform the sender to re-send email. 
   In case the sender is on the smtplist or the compromisedlist, the check can be performed if this sender needs to be moved to saseplist as follows. First, user&#39;s SASEP server (e.g. sasep1.userdomain.com) tries to establish communication with sender&#39;s SASEP server (e.g. sasep1.senderdomain.com) using unique message id of received email and unique authorization id generated by user&#39;s SASEP server as arguments. If a positive response is received within predefined time, sender&#39;s SASEP server is informed that sender&#39;s email address was moved to saseplist. Sender&#39;s SASEP server stores authorization id and name of user&#39;s SASEP server if sender will request later to undo movement to saseplist. User&#39;s SASEP server stores required information to be able to process such request as well. 
   In case the sender is on compromisedlist, sending of request for confirming that the received email was sent by this sender can be performed as follows. First, user&#39;s SASEP server sends email message to sender&#39;s email address requesting only reply to this email wherein Subject: field contains unique message id of received email and unique authorization id generated by user&#39;s SASEP server. If positive response is received within the predefined time, the received email is accepted. 
   In case the sender is not on any list, sending of challenge requesting results to accept received email can be performed as follows. First, user&#39;s SASEP server (e.g. sasep1.userdomain.com) tries to establish communication with sender&#39;s SASEP server (e.g. sasep1.senderdomain.com), using as arguments unique message id of received email, unique authorization id generated by user&#39;s SASEP server and challenge request. If positive response is received within the predefined time, the received email is accepted. If SASEP servers cannot establish communication, user&#39;s SASEP server sends email message to sender&#39;s email address using same arguments wherein Subject: field contains unique message id of received email and unique authorization id generated by user&#39;s SASEP server. If a positive response is now received within the predefined time, the received email is accepted. Otherwise, the received email is deleted. 
   The challenge can be computational challenge, human challenge, micro-payment request, and potentially some other mechanism. Computational challenge can be e.g. the product of two prime numbers where those two prime numbers are the result, but it can also be something else. Human challenge can be image that contains word easily readable by person and hardly readable by image-processing algorithms, link to some web page where a person has to perform some task, but it can also be something else. A combination of two or more challenges is possible. The purpose of this is that challenge can be solved both by a person and by automating mechanism. In such case, it is expected that only the correct response of one of them is required. 
   A solution when automating mechanism can solve challenge does not imply that this is suitable for sending Spam. The challenge can additionally depend on the probability that received email is Spam. 
   As additional security measure, lists instead of email addresses can contain email address&#39; signatures, where each email address needs a low computation effort for computing unique signature and for each signature it is an almost impossible effort to compute to which email it belongs. Accordingly, even if some hacker download lists, she/he will not be able to extract and potentially misuse email addresses. 
   With advanced client application or advanced SMTP server, private email address can be automatically added to Bcc: field of all outgoing email messages. Additionally, according to the automatic procedure to private email address only signatures of recipient email addresses and message-id can be sent. This can additionally decrease the effort each user has to use SASEP. 
   For enhancement of security in communication between two SASEP servers, additionally HTTP/SSL (HTTPS) protocol can be used. 
   Additional enhancement regarding email client and SASEP server is if at least one of them is able to perform computational task in background by using predefined percentage of processor power. Automating this task will additionally decrease the need for interaction from the users. 
   Advanced performance can be achieved by the functionality of SASEP server implemented jointly with the implementation of SMTP server. Also, SASEP server can be implemented as part of the hardware system like firewall, etc. 
   Also, it should be noted that hereby given principles can be applied when instead of email other types of messages are exchanged. 
   It is understood that many other modifications and variations may be devised given the above description of the guiding principles of the invention. It is intended that all such modifications and variations are considered to be within the spirit and scope of this invention, as defined in the following claims.