You can still use the Gmail UI with a custom domain for free. All you need is a mail server. Once it's set up, configure a free Gmail account to fetch your email with IMAP and send from your domain with SMTP. Now you own your email but still get the Gmail UI as long as you want to use it, for free, with the option to use any other client you want as well.
My experience with mail clients has been pretty poor in general. I haven't done a survey recently but all the others I've tried in the past have been slow too, and the search and spam filtering did not work as well.
Oh this is an interesting tip. Any guides? I'd imagine this could have deliverability problems being from a self-hosted mail server but maybe that's just been ingrained in me by email providers :)