Trouble sending to one domain

[SpAcKs]

I found 3 messages in the 'Deferred' section of the Mail Queues all going to the same address. However, I can't seem to find any good information on the message that it's showing.

lost connection with mail.domain.com[xxx.xxx.xxx.xxx] while sending RCPT TO

I've ran DNS checks on the domain and everything seems to checkout.

Where do you think I should start looking?

[uxbod]

Check /var/log/zimbra.log for more information. You could also try telneting to that server on port 25 and put through a manual message.

[SpAcKs]

I'm having the same issues with sending mail to one domain. Here's what I found in the zimbra.log;

Feb 24 15:08:03 mail postfix/qmgr[4115]: EBEA93FC76: from=<user@domain.com>, size=16087, nrcpt=2 (queue active)
$> <user2@domain2.com>,<user3@domain2.com> SIZE=16087 Received: from mail.doamin.com ([127.0.0.1]) by localhost (mail.domain.com [127.0.0.1]) (amavisd-new,$
Feb 24 15:08:03 mail amavis[14707]: (14707-15) Checking: gk5ULaX994aj [151.204.186.240] <user@domain.com> -> <user2@domain2.com>,<user3@domain2.c$
Feb 24 15:08:06 mail postfix/smtpd[23721]: connect from localhost[127.0.0.1]
Feb 24 15:08:06 mail postfix/smtpd[23721]: 14A6140021: client=localhost[127.0.0.1]
Feb 24 15:08:06 mail postfix/cleanup[23679]: 14A6140021: message-id=<027c01c996bb$88088400$98198c00$@com>
Feb 24 15:08:06 mail postfix/smtpd[23721]: disconnect from localhost[127.0.0.1]
Feb 24 15:08:06 mail postfix/qmgr[4115]: 14A6140021: from=<user@domain.com>, size=16422, nrcpt=2 (queue active)
Feb 24 15:08:06 mail amavis[14707]: (14707-15) FWD via SMTP: <user@domain.com> -> <user2@domain2.com>,<user3@domain2.com>,BODY=7BIT 250 2.6.0 Ok,$
Feb 24 15:08:06 mail amavis[14707]: (14707-15) Passed CLEAN, [x.x.x.x] [x.x.x.x] <user@domain.com> -> <user2@domain2.com>,<user3$
Feb 24 15:08:06 mail postfix/smtp[23719]: EBEA93FC76: to=<user2@domain2.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=3.2, delays=0.7/0.01/0/2.5, dsn=2.0.0$
Feb 24 15:08:06 mail postfix/smtp[23719]: EBEA93FC76: to=<user3@domain2.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=3.2, delays=0.7/0.01/0/2.5, dsn=2.0.0, s$
Feb 24 15:08:06 mail postfix/qmgr[4115]: EBEA93FC76: removed
Feb 24 15:08:06 mail postfix/smtpd[21686]: disconnect from static-x-x-x-x.east.comcast.net[x.x.x.x]
Feb 24 15:08:06 mail postfix/smtp[23588]: 14A6140021: lost connection with mail1.domain2.com[x.x.x.x] while sending RCPT TO
Feb 24 15:08:06 mail postfix/smtp[23588]: 14A6140021: to=<user2@domain2.com>, relay=mail2.domain2.com[x.x.x.x]:25, delay=0.51, delays=0.01/0/0.43/0.07, ds$
Feb 24 15:08:06 mail postfix/smtp[23588]: 14A6140021: to=<user3@domain2.com>, relay=mail2.dbi.com[x.x.x.x]:25, delay=0.51, delays=0.01/0/0.43/0.07, dsn=4$

Also, I seem to be timing out when I try to attempt a manual telnet email send on there server. However, I can't tell if I'm typing quick enough.

Are there any other logs that might show a bit more detail on the SMTP transaction?