Message failed: 451 4.3.5 <END-OF-MESSAGE>: End-of-data rejected: Server configuration problem

Hello,

Sometimes I get this error in the “Email” module:

Message failed: 451 4.3.5 : End-of-data rejected: Server configuration problem.

Most of the time it’s working, I can’t find out when/why the error is ocurring.

I’m sending some content:

and 2 attachments, 1 PDF and 1 XML file: