Postfix - Timeout transfering email with attachment

Good morning all!
I come to you with an issue on my mails on 1 of my UCS.
I host different UCS servers for different domains. I use an SMTP gateway in DMZ for all the domains and it works just fine.
I added a new server (UCS 4.3.430) a while ago, and noticed errors on the domain installed on this new server. I get timeouts when transfering emails with larger than 100kB.
All my other servers work fine but this one keeps dropping the connection with the SMTP gateway with timeout errors: dsn=4.4.2, status=deferred (conversation with 10.xx.xx.xx[10.xx.xx.xx] timed out while sending message body)
I have checked all the config files for Postfix on the new machine and the old ones, and there exactly the same. The only difference I can see is that the old servers have been build on 4.2 then upgraded, when the latest server has been built straight on 4.3.

Do you guys know where I should look to sort that out?

Thanks for your help!


I’d also check for differences regarding the network connectivity between the working systems and the box where you are facing the issue. I’ve seen those symptoms in cases related to MTU issues.
“The internet” also says that comparing and eventually increasing smtp_data_*timeout (postfix-)parameters on the sending side could be worth to try.



Thanks for your answer. I’ve seen this MTU thing too.
After extensive logging and debug, I am 95% sure the issue comes from the new box and not from the sender, as it works just fine to other recipients.
Do you know if there is an MTU setting somewhere in the UCS config? Maybe this could be changed and then fix my issue.

By the way, the 4.3 version already caused me quite a few problems (domian joining, computer adding to the domain, user rights…) that got fixed when starting the install from 4.2 and upgrade to 4.3.

I will keep digging into this timeout issue, and will let you know if I find anything.

Thanks for your help!!!