Are there any alternatives to mutt?

The obvious answer is Alpine, which used to be Pine, but was freed by the University of Washington. Pine is non-free software, Alpine is free software. Alpine is quite similar to Mutt, but Mutt is generally considered to be more powerful and flexible. The current active branch of Alpine is a fork called Re-Alpine, since the University of Washington has largely ceased development of Alpine as of 2008.

The Wikipedia pages on Pine and Alpine cover the history adequately.

I'd recommend trying to figure out your issues with Mutt instead of jumping to another mail client. Alpine inherits a polished user interface from Pine, but has some significant limitations and inflexibilities compared to Mutt. Therefore, you may find using it comes with its own problems.

Personally, I've used Pine since 1994, and switched to Alpine when that became available. I've thought over the years that I ought to be using Mutt instead, but never managed a successful transition.

Incidentally, IMAP was created by the late Mark Crispin, who used to work at the University of Washington developing IMAP. He was therefore also, unsurprisingly, responsible for Pine's IMAP support.

In the Pine credits he is listed thus:

C-Client library & IMAPd:       Mark Crispin

Check these out:

• sup — A curses threads-with-tags style email client
• aerc — Asynchronous email client for your terminal (slow development)

You might want to consider nmh, a set of programs for messing with mail. As each function is a separate command, you can mix and match, and combine them with any old Unix command/filter.

Never forget the venerable mail and Mail programs...