Clogged queue

Lately I've been getting messages from exchange saying there are a
large number of messages pending in the e-mail server. When I check, I
see 200 or 300 messages in the queue, waiting for retry or whatever.
When I check the properties, it says they are from
postmaster@xxxxxxxxxxxxx, and they are all to various addresses at the
same domain. What is happening here? We have relaying turned off of
course, but it looks like some sort of relaying is being tried. What
should I do?

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