[exim] Problems delivering to mac.com?

Is anyone else having persistent problems delivering to mac.com? I'm
getting very frequent defers from them, mostly:

defer (104): Connection reset by peer: smtp-mx.mac.com [17.250.248.49]

but occasionally also

defer (110): Connection timed out

The messages eventually deliver, often after several retries.

Here's an example from my logs:

2006-05-03 15:19:43 1FbMsw-0000Bv-Ig <= msherman@???
H=([192.168.1.117]) [207.139.16.74] P=esmtpsa
X=TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32 A=plain_saslauthd_server:msherman
S=1240 id=4459024C.1040308@???
2006-05-03 15:19:44 1FbMsw-0000Bv-Ig smtp-mx.mac.com [17.250.248.49]:
Connection reset by peer
2006-05-03 15:19:44 1FbMsw-0000Bv-Ig == user@??? R=dnslookup
T=remote_smtp defer (104): Connection reset by peer: smtp-mx.mac.com
[17.250.248.49]
2006-05-03 15:21:46 1FbMsw-0000Bv-Ig == user@??? R=dnslookup
T=remote_smtp defer (-53): retry time not reached for any host
2006-05-03 15:52:08 1FbMsw-0000Bv-Ig smtp-mx.mac.com [17.250.248.49]:
Connection reset by peer
2006-05-03 15:52:08 1FbMsw-0000Bv-Ig == user@??? R=dnslookup
T=remote_smtp defer (104): Connection reset by peer: smtp-mx.mac.com
[17.250.248.49]
2006-05-03 16:21:52 1FbMsw-0000Bv-Ig smtp-mx.mac.com [17.250.248.49]:
Connection reset by peer
2006-05-03 16:21:52 1FbMsw-0000Bv-Ig == user@??? R=dnslookup
T=remote_smtp defer (104): Connection reset by peer: smtp-mx.mac.com
[17.250.248.49]
2006-05-03 16:51:57 1FbMsw-0000Bv-Ig => user@??? R=dnslookup
T=remote_smtp H=smtp-mx.mac.com [17.250.248.49] QT=1h32m15s DT=11s
2006-05-03 16:51:57 1FbMsw-0000Bv-Ig Completed QT=1h32m15s

I don't currently seem to be having trouble delivering to any other
servers -- in fact, every single instance of "==" in my current week's
rotation of mainlogs are for mac.com. Any suggestions?

- Marc