Use email.headerregistry classes?

The headerregistry classes [1] look useful for parsing, especially for address types which are rather complicated.

In particular the AddressHeader handles multiple addresses, and splits the address into display and email.

MessageID was added in 3.8, but does not trim leading spaces. That is trivial to fix.

[1] https://docs.python.org/3.7/library/email.headerregistry.html

Start with the linked Python email.headerregistry documentation, especially AddressHeader and MessageID, then locate the Pony Mail code that parses address and message-ID headers. Determine which parsing paths should use these classes and verify that leading spaces are removed from MessageID values; the issue names no files or tests.

Written by the indexing model from the issue text.