Can't get your email to go plain text, attachments work. If they don't, why not change providers? It's a bit of work, but almost anyone can setup their own email server for next to nearly free.
That is not as easy as it was, mainly because of IP reputation. If you have your own MX and outbound MTA/MSA you will have to go through painful processes of getting out of blacklists, and even then your outgoing messages might end-up in users' spambox. The game has changed, and it's for us old-timers that life is rough, already.
