There is indeed a version for MacOS. In fact, there are three:

Eudora Lite - freeware, but (to my mind) kind of limited
Eudora Pro (sponsored mode) - also freeware, but a full-blown, nicely designed mail client. The only catch is you have little ads down in the corner of your screen. All the functionality is available.
Eudora Pro (full version) - Same as the previous, but with no ads. I don't remember what I paid, but I was so delighted with Eudora that I paid gladly. (I was looking for a substitute for OE.)

There's also a version that runs on OS X. You can even use your OS 9 settings files so you have seamless transition between 9 and X.