Tests do not check the parsing policy

The tests use mbox.get(key) to before passing the message to the achiver code.
This implicitly uses the compat32 policy to parse the message.

The tests currently bypass the part of the archiver that uses the policy.

Start by locating the tests that call mbox.get(key) and the archiver code that applies the parsing policy. Run the affected tests to confirm they supply a pre-parsed message using compat32. Done means the tests cover the archiver's policy-handling path rather than bypassing it.

Written by the indexing model from the issue text.