SMTPGuard is a tool which controls the flow of email traversing an MTA (Mail Transfer Agent). It is designed to be used on an SMTP server for incoming mail, and currently supports postfix.

SMTPGuard was originally created to meet the needs of Internet Service Providers (ISPs). ISPs typically receive tremendous amounts of email from their local (user) network.

Within a wide variety of users, some are spammers, many unknowingly have virus infected PCs; each of these can send large quantities of mail through the ISPs SMTP (Simple Mail Transfer Protocol) servers.

This is especially a problem for ISPs who are connected to their users via high speed lines such as fiber or ADSL. SMTPGuard was developed to prevent SMTP servers from being overwhelmed by unexpected spikes in usage from specific (often malicious) users.

For a large ISP, their only problem isnt just with overloaded incoming SMTP servers. SPAM will also be queued on the outgoing server (perhaps the same server) for delivery to the Internet.

Because the mail is SPAM it will likely bounce, then double bounce putting extreme load on the outgoing server and its queue. smtpguard is designed to stop this type of extreme load by stopping floods of mail at the gate (incoming server).

SMTPGuard is point based. Each time a client connects to the SMTP server, SMTPGuard adds points according to the rules file. SMTPGuard uses information acquired during the SMTP session, adds points according to the rules file, and finally takes actions based on its settings. For example, the information below is used:

- Remote IP Address
- Character string provided by MAIL FROM command
- Character string provided by RCPT TO command


The following actions can be taken:

ok - white list
wait - delay processing
reject - reject messages
mail - send alert email to administrator
log - output message to log
delete - delete record in database

Whats New in This Release:

· postfix/flexguard.c: remove word flexguard. use smtpguard instead. rename filename to postfix/smtpguard.c
· postfix/Makefile.am: rename flexguard -> smtpguard
· configure.in: 1.1.1
· rename FLEXGUARD_{CFLAGS,LIBS} -> SMTPGUARD_{CFLAGS,LIBS}
· smtpguard/Makefile.am,postfix/Makefile.am,test/Makefile.am: Ditto
· debian/postfix-smtpguard.files: added
· README.postfix: added