Please fill in this template when reporting a bug, unless you know what you
are doing.
Description of Problem:
It seems, that mail filters work on parsed mail. Trying to create filter
based on mail source, it fails.

Steps to reproduce the problem:
1. Create a filter containing Mail body contains (or regexp for body)
"Content-Type: application/x-zip-compressed".
2. Get a mail containing ZIP file (with exactly this substring in mail source)

Actual Results:
Mail is not filtered.

Expected Results:
Mail is filtered.

How often does this happen? 
Every time

Additional Information:
If it is expected behavior, new filters "Mail source contains" and "Regexp
for mail source" would be nice.