This is Debian bug #785380.
In short: the traptoemail Perl script emits a locale-dependent Date header, which does not conform to RFC 5322 in general. This happens because strftime() is locale-dependent, and could be solved for example by temporarily resetting the locale to C for the strftime() call.
The simplest solution is probably just to drop generating the Date header all together and leave it to the MSA to fill it in.
What do you think?
I totally agree.
patch with possible solution. May I ask for review/accept?