4.3. Mailman's internal archiver (Pipermail) doesn't understand MIME! What can I do?
Mailman 2.0.* uses a version of Pipermail to archive messages that doesn't understand MIME. If upgrading to Mailman 2.1.* is not an option, there's not much you can do about this other than using an external archiver.
Suggested external archivers:
MHonArc is probably the most commonly used, and is certainly the most flexible and configurable of the current Open Source mail archivers.
Example MIME messages archived under MHonArc:
One of the other significant advantages of MHonArc is that it properly renders and displays messages written in national charactersets. This can be particularly valuable/important for non-english lists and authors.
Converted from the Mailman FAQ Wizard
This is one of many Frequently Asked Questions.