I am so disappointed. I can't believe that the great and powerful Microsoft, the 800-pound gorilla in the room, has taken classic outlook and botched it up so badly with this new outlook. So many things don't work properly.
I am having the same problem because I build tables to quote customers pricing in Word and then try to copy/paste it to an email. The rows expand to three times the original size and the and there's nothing I can do about it.
And designing and building templates? forget about it. If you need to embed graphics into the email like a line card or price list, you simply can't do it. The 'my templates' app
gives you a tiny little space to put your content in. You should be able to open an email, set it up as if you were using a page layout program and then simply save it as a template.
I pay yearly for Microsoft 365, And this is really sad. I'm sure they thought they road tested this to make sure everything was cool, but they should have spent a little more time seeing if people would be happy with it the way it is.