[CentOS] Re: Kind of OT: internal imap server

Feizhou feizhou at graffiti.net
Fri Sep 1 06:30:47 UTC 2006

> Sendmail chats on sockets with the milter process and thus
> doesn't become any larger.  And the milters can be written
> in any language.  Mimedefang uses a combination of C and
> perl.  If you are going to run spamassassin you are stuck
> with perl regardless and that's going to be your slow step
> anyway so you might as well have it pre-loaded and use it
> as the parser for your control steps.

Hence why I have spamassassin used to filter after the mail is queued. 
Do you make mimedefang run spamassassin on all your mails before queueing?

>> sendmail's fork a process per connection + perl in some situations make 
>> people have nightmares whereas the same could be done in a much more 
>> efficient manner especially with postfix. 
> Like I said, most people don't bother to understand how it
> currently works.  Sendmail runs one milter process which
> all the sendmail processes use via socket connections. In
> MimeDefang's case the controlling milter is written in C
> and runs multi-threaded, multiplexing connections to some
> small number of slaves that do the work in single-threaded
> perl.  There is no extra fork per sendmail involved and
> a much smaller number of perl processes than sendmails.
> Also, the multiplexer manages the slave processes by
> restarting them if they crash or exceed memory limits
> and will inform sendmail to retry on timeouts.

Okay, I get it. lotsa sendmail processes < (one socket per sendmail 
process) > single milter process < ? > perl processes

> Any way you look at it, it is a much nicer design than
> making the receiving process handle everything itself
> or fork additional processes per message or run.

postfix does it similarly. smtpd does not handle everything itself. 
You've got cleanup and trivial-rewrite to handle some stuff for smtpd 
and they also pass some stuff out to proxymap to handle. Really light 
stuff are handled by smtpd and the more heavy stuff is parceled out to 
cleanup, trivial-rewrite and proxymap to handle.

>> sendmail + mimedefang is overrated. Now that postfix 2.3 is the stable 
>> line now...postfix + mimedefang will probably be interesting depending 
>> on how it is done...
> We can pick up the discussion when/if some large volume users
> equivalent to those on the MimeDefang list start using it.  A
> big value in using existing, working software is that you can
> take advantage of other's previous experience with it.


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