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Secondary MX user list filter for Sendmail

  • From: Todd Vierling
  • Date: Tue May 18 21:27:18 2004

A colleague asked me offlist about how to make a Sendmail secondary MX
properly return 550 for invalid recipient addresses.  For smaller sites --
or even larger sites if the list is autogenerated and the access_db uses
"btree" storage (it's rather fast) -- the below solution will do just that.


In your secondary MX's, add the following FEATUREs if you don't
already have them.


Rebuild your from this, and then put entries like the following
in your /etc/mail/access file (assuming "" is your domain).  I'm also
assuming that "" is already in /etc/mail/relay-domains (or
/etc/mail/sendmail.cR depending on your sendmail install), so that relayed
mail can get through.                    RELAY                    RELAY                         "550 User unknown"

The RELAY lines designate explicitly allowed recipient addresses for
relaying to the primary MX.  The To:...550 line, which requires the
"blacklist_recipients" feature, is a fallback rule that matches after the
email addresses and returns the expected "User unknown" error.

Now rebuild your access.db file, restart sendmail, and voila, you have a
secondary MX explicit user list.

-- Todd Vierling <> <>

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