[CentOS] Sendmail burst of "rejecting connections" - why?

What's the reason for the burst of sendmail complaints below?

My CentOS 4.3 server only handles internal mail for my small network.
It doesn't handle Internet mail at all, so I guess I can't blame a
crack attempt for this.  IPTables rules should prevent external
connections to everything except SSH's port 22.

I've looked through the other logs hoping that some other activity would
be seen at this time as well.  Nothing.  the surrounding entries in
/var/log/maillog are perfectly reasonable.  As far as I can tell this
14-minute burst of sendmail activity exists in isolation.

Can anyone suggest a reason for these log entries?

Thanks.

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May 25 07:09:24 server sendmail[2942]: rejecting connections on daemon MTA: load average: 24
May 25 07:09:39 server sendmail[2942]: rejecting connections on daemon MTA: load average: 25
May 25 07:09:54 server sendmail[2942]: rejecting connections on daemon MTA: load average: 26
May 25 07:10:09 server sendmail[2942]: rejecting connections on daemon MTA: load average: 29
May 25 07:10:24 server sendmail[2942]: rejecting connections on daemon MTA: load average: 31
May 25 07:10:39 server sendmail[2942]: rejecting connections on daemon MTA: load average: 32
May 25 07:10:54 server sendmail[2942]: rejecting connections on daemon MTA: load average: 33
May 25 07:11:24 server last message repeated 2 times
May 25 07:11:39 server sendmail[2942]: rejecting connections on daemon MTA: load average: 34
May 25 07:12:24 server last message repeated 3 times
May 25 07:12:39 server sendmail[2942]: rejecting connections on daemon MTA: load average: 34
May 25 07:12:54 server sendmail[2942]: rejecting connections on daemon MTA: load average: 33
May 25 07:13:09 server sendmail[2942]: rejecting connections on daemon MTA: load average: 32
May 25 07:13:24 server sendmail[2942]: rejecting connections on daemon MTA: load average: 31
May 25 07:13:54 server last message repeated 2 times
May 25 07:14:09 server sendmail[2942]: rejecting connections on daemon MTA: load average: 30
May 25 07:14:54 server last message repeated 3 times
May 25 07:15:25 server last message repeated 2 times
May 25 07:15:40 server sendmail[2942]: rejecting connections on daemon MTA: load average: 29
May 25 07:15:55 server sendmail[2942]: rejecting connections on daemon MTA: load average: 29
May 25 07:16:10 server sendmail[2942]: rejecting connections on daemon MTA: load average: 28
May 25 07:16:25 server sendmail[2942]: rejecting connections on daemon MTA: load average: 27
May 25 07:16:40 server sendmail[2942]: rejecting connections on daemon MTA: load average: 26
May 25 07:16:55 server sendmail[2942]: rejecting connections on daemon MTA: load average: 25
May 25 07:17:10 server sendmail[2942]: accepting connections again for daemon MTA
May 25 07:17:45 server sendmail[2942]: rejecting connections on daemon MTA: load average: 24
May 25 07:18:00 server sendmail[2942]: rejecting connections on daemon MTA: load average: 25
May 25 07:18:15 server sendmail[2942]: rejecting connections on daemon MTA: load average: 27
May 25 07:18:30 server sendmail[2942]: rejecting connections on daemon MTA: load average: 28
May 25 07:18:45 server sendmail[2942]: rejecting connections on daemon MTA: load average: 29
May 25 07:19:00 server sendmail[2942]: rejecting connections on daemon MTA: load average: 30
May 25 07:19:45 server last message repeated 3 times
May 25 07:20:00 server sendmail[2942]: rejecting connections on daemon MTA: load average: 29
May 25 07:20:15 server sendmail[2942]: rejecting connections on daemon MTA: load average: 28
May 25 07:20:45 server last message repeated 2 times
May 25 07:21:00 server sendmail[2942]: rejecting connections on daemon MTA: load average: 25
May 25 07:21:15 server sendmail[2942]: accepting connections again for daemon MTA