[Exim] msglog creation while testing with "exim -bh"

I've been testing ACLs in an exim 4.30 configuration I'm building by piping messages into "exim -bh".

I've noticed that if the test SMTP session finishes with a "250 OK", it writes a msglog file with a "Received from" line in it.

Given that this is just SMTP testing, I was wondering whether it shouldn't be creating the msglog file, which will now remain unless someone comes along and deletes it?

Cheers,
Matt.