As is usual for me, this is a long story, and it’ll take a little while for me to get to the point.
So, n the days of the Classic Mac OS, which seems a century ago (and more or less it was), I used Claris Emailer as my email client of choice. It was originally created by Fog City Software and acquired by Apple’s subsidiary Claris, which also (and still) publishes FileMaker.
I settled upon Emailer because of its support not just for regular Internet email, but to such online services as AOL and CompuServe. Indeed, it was reportedly the only email client licensed to manage AOL. As a former member of AOL’s forum staff, at the time this was the best possible solution.
To me, the features beyond the basics were not important. Being able to manage my growing collection of messages was upfront and center.