During the processing of the emails Amavis-new conducts a series of tests, including so called bad-header checks which usually give a headache to system engineers because of false detections (most commonly a missing required header field or 8-bit encoding, etc)

Since version 2.4.4 of Amavis-new, you can actually tweak the bad-header tests instead of turning them completely off.

There is an $allowed_header_tests variable by which you can define what should be looked up during the bad-header checks, and the list is as follows:

other     catchall for everything else - normally not used
mime      Bad MIME (sub)headers or bad MIME structure
8bit      Invalid non-encoded 8-bit characters in header
control   Invalid control characters in header (CR or NUL)
empty     Folded header field made up entirely of whitespace
long      Header line longer than RFC 2822 limit of 998 characters
syntax    Header field syntax error missing Missing required header field
multiple  Duplicate or multiple occurrence of a header field

So, the final solution is to insert the aprropriate lines in the /etc/amavisd/amavisd.conf file, globally or in the appropriate block setup. For example:

$allowed_header_tests{'8bit'} = 0;
$allowed_header_tests{'missing'} = 0;

…would exclude missig items (the infamouse Date missing) and 8bit tests form the header check process.