If you're running Windows, try Pegasus Mail[1], it's a contemporary of Eudora, but is still maintained, and supports UTF-8. Releases are pretty infrequent of late, but email is still email, so things still work. :)

[1] http://www.pmail.com/

I think the spiritual successor to Eudora is MailMate. Barebones functional UI, tons of features (many hidden or needing some end user work to expose or make use of).

http://freron.com

I sometimes think I'm one of the few people happily using Mozilla Thunderbird. It hardly ever seems to come up in these recommendations and when it does, it's usually accompanied by plenty of criticism about it not being updated regularly enough. But I'm happy using it for 5 email accounts and the ability to copy the entire profile folder to a new PC (or even use it directly from a USB stick if you're that way inclined) has been really handy for me in the past. The same profile folder can even be shared between 2 different OS's!

I was in the same boat until I moved go Google apps for domains, and imported my Eudora content.

My mother is in the same boat right now, and looking for suggestions. UTF-8 and prevalence of HTML content are making it nearly impossible to keep using in this day and age.

Best features (not killer but very nice) are/were the storage format, and saving attachments externally, and not "in line" with the message.

[Disclosure: I'm a co-founder]

If you're open to new approaches to email you should try Unibox. It's an email client for Mac (and soon iOS) that lets you browse through your emails by person, so you always have all messages and all attachments with a person in one place.

https://www.uniboxapp.com

I still love and use Seamonkey. It's a mozilla-based product that is the modern heir of the old Netscape Communication Suite. You get a browser that is based on the latest Firefox but not dumbed down as Firefox is, an email client very similar to Thunderbird, an IRC client etc., all in a single package.

Depends on what you want. If you want a graphical client, try Thunderbird or Evolution, depending on if you need Windows support. If you want a powerful client for processing a large volume of mail, and you don't mind needing separate tools to handle HTML mail, then try mutt.

I was a long time Eudora user -- I moved to Thunderbird a long time ago and I'm still using it. There aren't really many reasonable desktop mail clients anymore.