[Exim] Sporadic routing problem

I'm running an exim server on Mac OS X -- it takes mail, runs it through
SpamCheck, and then sends it on to the local OS X mail server, running on
the same server but on a different port.

I'm having an occasional problem with messages being rejected because an
address (mine, specifically) is unroutable. It happens with my and 2 other
e-mail addresses, but not with the other 2 dozen or so.

Most of the time mail delivery is fine, consistent, but sometimes it's not.

Has anyone else had this problem, and can suggest something?

Here's a snip from exim_mainlog, taken this morning and greped for my
username. You'll notice two messages that weren't delivered, one at the top
and one at the bottom; and all the rest were. Both messages were resent
within minutes, and delivered fine:

2003-08-22 10:18:08 HK0YE4-000F73-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 10:19:15 H=dolly1.pobox.com [207.106.49.22] F=<Reebs924@???>
rejected RCPT <marlier@???>: Unrouteable address
2003-08-22 10:19:21 H=dolly1.pobox.com [207.106.49.22] F=<> rejected RCPT
<marlier@???>: Unrouteable address
2003-08-22 10:22:10 HK0YK4-000I7M-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 10:22:10 HK0YK2-000I74-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 10:22:30 HK0YKN-000IH9-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 10:22:30 HK0YKL-000IEK-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 10:39:22 HK0ZCQ-00048K-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 10:46:35 HK0ZPL-000BBJ-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 10:46:35 HK0ZPJ-000BAW-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 10:46:36 HK0ZPL-000BBS-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 10:46:36 HK0ZPJ-000BAX-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:11:07 HK10TO-000I3G-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:11:07 HK10TN-000I3C-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:11:27 HK10U7-000I3L-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:16:41 HK112Z-000I6T-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:16:41 HK112X-000I6N-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:16:42 HK112Z-000I70-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:16:42 HK112Y-000I6O-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:19:05 HK116Y-000I7S-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:19:05 HK116X-000I7M-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:19:06 HK116Z-000I80-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:19:06 HK116Y-000I7O-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:19:07 HK1170-000I88-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:19:07 HK116Z-000I7X-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:19:09 HK1172-000I8H-00 => marlier@???
R=localuser T=local_delivery H=127.0.0.1 [127.0.0.1]
2003-08-22 11:19:09 HK1171-000I8D-00 => marlier <marlier@???>
R=spamcheck_router T=spamcheck
2003-08-22 11:25:51 H=icicle-214-2.pobox.com (icicle.pobox.com)
[207.8.214.2] F=<info@???> rejected RCPT
<marlier@???>: Unrouteable address