I have a love-hate relationship with Mac Mail... mostly hate. The one good thing about it is that it's fairly easy to do the initial setup of an account in the app, and most ISPs provide easy solutions for that.

I use a lot of different email addresses (created with my own domain names) to help minimize spam, and to organize categories of email, as well as provide easy exit strategies when I want to close down a channel of communication. I also use temporary disposable forwarding addresses, which are easy to delete when they get compromised, shared without permission, or senders refuse to honor my unsubscribe requests.

Every couple of weeks, Mac Mail will just forget the settings for an account, and I start getting these super-annoying "Can't find server" errors. Then I have to get elbows-deep in settings and correct port numbers, test server connections, etc. I have even had to just delete an account and set it up again from scratch a couple of times -- not a disaster since I usually use IMAP accounts and the messages are saved on the server, but it's a maddeningly huge time-waster!

I have used Thunderbird in the past, as well as Airmail, Canary, Spark, Seamonkey, and a couple of others I'm forgetting at the moment. Despite my annoyance with Mac Mail, I have a lot of messages stored in it -- some of which don't exist anywhere else except in backups (and MANY of which I should delete, but that's another story...) -- so it's not that easy to just switch to something else at this point. I may give Thunderbird another look, though.