Anyone willing to help me with this packet capture?

[Jeremy Fowler]

Trying to figure out why this particular domain is unable to send large
emails (i.e. attachments) to our domain. Small emails go through fine.
However, these large emails get stopped by postfix with "lost connection
after DATA from xxx" errors. I'm thinking a possible MTU error or some other
weird network/router issue.  Seems to be only happening from this one
domain.  anyone willing to give me a hand?  Thanks in advance!

Postfix errors:

Dec  3 12:34:12 gauntlet postfix/smtpd[23895]: connect from
gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:12 gauntlet postfix/smtpd[21773]: connect from
gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:12 gauntlet postfix/smtpd[23895]: 741843CD643: client=
gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:12 gauntlet postfix/smtpd[21773]: 768C13CD644: client=
gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:15 gauntlet postfix/smtpd[23895]: lost connection after DATA
from gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:15 gauntlet postfix/smtpd[23895]: disconnect from
gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:16 gauntlet postfix/smtpd[21773]: lost connection after DATA
from gateway02.websitewelcome.com[69.56.184.20]
Dec  3 12:34:16 gauntlet postfix/smtpd[21773]: disconnect from
gateway02.websitewelcome.com[69.56.184.20]
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