[SATLUG] Sendmail sending twice?

Brad Knowles brad at shub-internet.org
Thu May 29 16:26:16 CDT 2008

David Salisbury wrote:

> Has anyone on the list dealt with a problem where sendmail seems to be
> sending some messages twice?  This seems to be happening only with
> messages with larger attachments, but not all of the time.  I have
> checked sendmail's logs, and it IS actually creating two different
> messages with two different message IDs, within about 2 seconds of each
> other.  But I know the mail client is just sending it out once.  Has
> anyone else experienced this, or have any ideas how to stop it??  My
> Google searching so far has been fruitless.

Sendmail works really hard to try to avoid duplication.

The only two types of case I know of where sendmail might potentially send 
more than one copy would be if it was transmitting a copy of a message, got 
all the way to the end, and then got an error message back from the other 
side saying that the transmission failed, when in fact the remote end had 
actually gone ahead and delivered the message but returned a spurious error.

Or if sendmail got a timeout on the final acknowledgement that the message 
had been accepted, so it assumed the other side did not get the whole 
message when that's not the case.

The other case where you might see something like this would be if the 
recipient was actually sending just one copy to an address on the sendmail 
server, but then that address was configured to forward to two separate 
addresses, and there are a variety of different ways you might get multiple 
deliveries -- think aliases, forwarding, etc....

Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>

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