[Mimedefang] Make Relay Servers Queue

Joseph Brennan brennan at columbia.edu
Wed Mar 28 12:23:41 EDT 2007

--On Wednesday, March 28, 2007 10:04 -0500 Bob Covell <bcovell at rolet.com> 

>> Sendmail does queuing.
>> It sounds like your relays depend on the primary for something.  Do they
>> need to ask it what recipients are valid?
> Yes, they do validate recipients with the backend servers.  So some sort
> of "ping" needs to go before this to validate that the servers are there?
> If not queue it?  I assume the queue would have to be initiated by MD,
> correct?

No, sendmail does queuing, when it has accepted a message and cannot
re-send it to the destination.

The problem in a nutshell is that when the backend is down, your relays
can't tell that any addresses are valid, so they don't accept any mail.
If they tempfail in that situation, at least you have a working system.

This is the tradeoff.  What you're doing means that you can create a
user on the backend, and you're done; the relays will discover the user
when mail comes in.  The alternative is to do more work when creating
a user, like adding the user to an ldap database, or to an aliases file
on the relays, so that the relays can function independently of the
backend.  Your choice.

Joseph Brennan
Lead Email Systems Engineer
Columbia University Information Technology

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