Pegasus did age well (if albeit very slowly). Most features you wanted to see in a modern mail client arrived eventually. There was a period of time where development had stopped IIRC because the developer didn't see the purpose in it anymore. Again IIRC he started again after seeing that the community wanted it to be kept alive.

I haven't seen a version in about 2 years now as my last client finally moved off of it due to the desire for 'cloud' style email and Blackberry support but Pegasus never let them down while they were on it.

I stopped using it around a decade ago because it was too slow when my mailbox got really huge, and it didn't have indexed search.

I'm curious how it's improved, but gmail is good enough that I have a hard time imagining wanting to go back to a desktop client.