SMC anti-spam e-mail filter
SMC anti-spam e-mail milter (plug-in) is an software application designed
to significantly reduce the amount of SPAM/UCE (junk-mail) you receive.
SMC uses a greylisting like technique to stops the junk-mail and a
set of dynamic auto "whitelists" for unknown, but legitimate senders.
[PAD 2.0]News
2008-06-30: Version 2.1 released. Added classic
SPF
support (file spf.c), add 'classicspf' option in config file (enabled by default). Fixed potencial bug
in cache algorithm. Configuration reload added on signal 1 (SIGHUP). Updated
FreeBSD startup script (file smc-milter.sh). "NS Relay" algorithm renamed to
AutoSPF.
Auto-confirmation algorithm renamed to AutoSWL (Auto Sender White List).
AutoSPF algorithm optimization.
Small bug fix in
AutoSPF code. Add new 'autospf'
and 'autoswl' options in config file. Bug fix in greylisting code. Minor changes
to config defaults. Check return codes, various potential bugs fixed. {client_addr}
and {client_name} macros are no longer required. Added 'pidfile' parameter
in config file to define the new pid file location if required. Added
'database' parameter in config file to change the default location of
filter database file location. Code cleanup and optimization. Documentation fix.
SMC Algorithms
SMC uses 3 original algorithms, one of which is
AutoSPF (Check relay by NS)
simulates a dynamic whitelist and will always accept the messages from
mail systems satisfying to following conditions:
- Mail domain name (the host part of the sender's e-mail address) must have an MX records;
- Mail domain name and the connection host address must be resolved;
- Connection host must be listed at the one of nameservers which hold the sender's mail domain name.
The second from the developed algorithms is a greylisting like algorithm or
"check delays" which is based on statistical check of delivery delays,
generated by a [tempfail] return code, that allows to exclude a direct
receiving of a mail, which not passed through the standard mail server.
NOTE: Using this feature the delivery of the mail from unknown, but
legitimate senders will be delayed for a count of 5-minutes checks,
which setted by the "maxcount" configuration parameter.
And the third of original algorithms is AutoSWL (Auto Sender White List) or "auto-confirmation" algorithm:
The sender of a "mail contact" (sender-recipient pair) means as
authenticated (whitelisted) if the filters statistics module has
registered the both of a sended forward (request) and a received
backward (reply) messages of this contact. The messages from the such
authenticated senders will never be delayed by the previous greylisting
algorithm.
SMC Headers
SMC will tag the incoming messages with the next set of traditional and widely used headers:
X-Spam-Flag: [YES/NO/WARN/PASS]
X-Spam-Report: System report which explains the reason of a Spam-Flag value apropriation.
X-Spam-Checker-Version: SMC-milter [Program Version]
X-Virus-Scanned: Name of virus scanner if enabled
For example:
X-Spam-Flag: NO
X-Spam-Report: Host 195.206.40.177 is related to lust.icc.ru.
X-Spam-Checker-Version: SMC-milter 2.0
X-Virus-Scanned: ClamAV using SMC-milter