mail_from.is_resolvable plugin

This plugin checks that the domain used in MAIL FROM is resolvable to an MX record.


This plugin uses the INI-style file format and accepts the following options:

  • timeout
    Default: 30
    Maximum limit in seconds for queries to complete. If the timeout is reached a TEMPFAIL is returned to the client.
  • allow_mx_ip=0|1
    Allow MX records that return IP addresses instead of hostnames. This is not allowed as per the RFC, but some MTAs allow it.
  • reject_no_mx=0|1
    Return DENY and reject the command if no MX record is found. Otherwise a DENYSOFT (TEMPFAIL) is returned and the client will retry later.
    DNS errors always return DENYSOFT, so this should be safe to enable.