> We use postfix as a mail queue / sending service in one of our
> applications. This application generates emails with PDF attachments. Some
> of the emails with PDFs get sent fine, but others seem to cause a "timeout
> after DATA" error.
> Through reading online, I've seen answers such as adjusting the MTU size on
> the network interface, etc. None of these solutions have worked. Has anyone
> had this happen, do you have any suggestions to fix it?
To diagnose the problem, make a packet recording, and have it
reviewed by an expert who can use that to determine if the problem
is with the sender, receiver, or in-between. That's more effective
than making random black-box changes.