Well the problem is simple, just from nowhere I started having problems with emails (spam filter Maia Mailguard) MIME::Parser version 5.420

more than 50% of all emails including legitimate are showing

WARN: MIME::Parser error: unexpected end of preamble

and therefore body for those emails is discarded, only the headers get through.

And this is happening in rounds, for example no problems for 4 hours and then for 5 to 30 minutes almost all of email is getting the same MIME::Pareser preamble error.

I'm out of ideas, maybe someone can guide me what to do next.