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]