Error "TypeError: str() argument 2 must be str, not bytes" when archiving Mailman list.

Symptoms

When archiving a Mailman mailing list the following error occurs:

TypeError: str() argument 2 must be str, not bytes" when archiving Mailman list.

Description

This error can be caused by a message's character set not being properly parsed during archiving.

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-47029. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

There is no available workaround at this time.