I used some good emacs mail client up to 1995, then the need to read Office attachments made me switch to some Windows client. HTML messages were not a thing yet. The switch was a regression in functionality for at least ten years, up to outbound filters in Thunderbird.

Edit: third question, how do you read mail on your phone? A couple of questions for the author. How do you handle attachments and do you download mail over POP3/IMAP or do you have your own server (hence SpamAssassin) ?