On 8/13/26 20:17, Bill Cole via Postfix-users wrote:
On 2026-08-13 at 12:41:08 UTC-0400 (Thu, 13 Aug 2026 18:41:08 +0200)
Matus UHLAR - fantomas via Postfix-users <[email protected]>
is rumored to have said:
On 13.08.26 15:48, Peymaneh Nejad via Postfix-users wrote:
[...]
The spamassassin documentation does not provide any hints on its usage/configuration as a
"delivery agent"
spamassassin is only a mail filter, it does not receive nor deliver mail.
Correct. It exists both as a suite of Perl modules that other programs (like
Milters) can load and a 'spamd' executable which runs as a daemon and accepts
connections on either a TCP port or a unix-domain socket by clients speaking a
simple protocol to have it check messages. A very simple sample client named
'spamc' is included, which is widely used by other programs to check messages,
rather than using the Perl modules themselves. Neither spamd nor spamc nor any
of the other tools in the SpamAssassin distribution understand how to deliver
mail in any way. A message check by SA only returns a message score and
optionally message headers to add.
You need a glue application that pushed mail to spamassassin and back.
Common glue apps are amavis, spamass-milter, rspamd.
The best list of glue choices is at
https://cwiki.apache.org/confluence/spaces/SPAMASSASSIN/pages/119543772/IntegratedInMta but a lot
of people with minimal volume can get away with using the Postfix "content-filter" or
"pipe" interfaces with very simple shell scripts using either spamc or even running the
spamassassin Perl script (which imposes a costly overhead) and then re-injecting a modified message
back into the mail delivery cycle using the 'sendmail' binary.
Thanks a lot to both of you! That made it much clearer to me.
You assumed correctly that the mail is reinjected via sendmail:
```
spamassassin unix - n n - - pipe
user=spamd argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -oi -f ${sender}
${recipient}
```
your glue application causes mail being reinjected to postfix the way it get's
DKIM-signed.
This is a common issue with "simple" content filters which follow the example
in the Postfix FILTER_README.
With OpenDKIM, the solution is to set "Domain" correctly and use the KeyTable+SigningTable
mechanism rather than a simple KeyFile. If you can't figure out why OpenDKIM is signing a message, set
"LogWhy" to "Yes" in its configuration and restart it for enlightenment.
I will look into that. Thank you!
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