How do I integrate MIMEDefang with OpenSMTPD?
OpenSMTPD has supported the Milter protocol since version 6.7.0. MIMEDefang can be used as a Milter filter with OpenSMTPD.
The socket OpenSMTPD connects to is the Milter socket created by mimedefang. It is set via the -p option of mimedefang (not via a wrapper-script variable). The separate multiplexor socket (used internally between mimedefang and its Perl workers) is set via -s on mimedefang-multiplexor and -m on mimedefang. See mimedefang(8) and mimedefang-multiplexor(8) for details.
Step 1: Start mimedefang-multiplexor and mimedefang with explicit socket paths, for example:
mimedefang-multiplexor -s /var/spool/MIMEDefang/mx.sock [other options]
mimedefang -p unix:/var/spool/MIMEDefang/mimedefang.sock \
-m /var/spool/MIMEDefang/mx.sock \
-U defang [other options]
If you installed from a distribution package, a configuration file may already be present at /etc/sysconfig/mimedefang (RPM-based systems) or /etc/default/mimedefang (Debian-based systems). If it exists, set the socket paths there rather than editing the startup script directly.
Step 2: Add a filter definition to /etc/mail/smtpd.conf, using the same path passed to mimedefang -p:
filter mimedefang proc-exec "filter-milter unix:/var/spool/MIMEDefang/mimedefang.sock"
If your OpenSMTPD version uses the older filter syntax (6.7.x), declare the Milter filter with:
filter mimedefang milter socket "unix:/var/spool/MIMEDefang/mimedefang.sock"
Step 3: Apply the filter to your SMTP listener(s):
listen on all filter mimedefang
Step 4: Ensure the _smtpd user has read/write access to the MIMEDefang socket directory.
Step 5: Check and reload the configuration:
smtpd -n && rcctl reload smtpd
Note that OpenSMTPD's Milter support covers a subset of the full Milter API. Features that rely on SMFIF_CHGFROM (envelope sender rewriting) or SMFIF_ADDRCPT_PAR may not be available on all OpenSMTPD versions.