Thank you for your reply.
Yes, this happens for every job, not just Exchange.
It seems to happen for every line that is greater than 74 characters in length. The system doesn't generate many messages where a single line is significantly longer than 74 characters so I've never noticed before if this happens in other positions past the 74th character. Checking just now, I found a message where it happened at the 74th and 148th (2x74) characters.
It doesn't seem to have any effect on the Backups: I can restore files and verify their integrity via MD5 checksums. I have to write multiple mail rules to properly sort these messages, though.