You might want to advise them that the Internet (RFC) standard (and quasi requirement) is that email text is in "plain-text" format with no special formatting.
I'm fully aware that many (most) people don't know this. And they use whatever formatting they want to. The risk, of course, is that your email might arrive at it's destination to a user who does not have the ability to read it. Like if they don''t have MS Word, for example. That's why the Internet standard is plain-text.
Anyway... you might also want to consider another email client form the market. I suppose they probably support different fonts. I don't know. I always set my configuration to "plain-text" regardless of the email client I'm using, for Internet work. When I use an email client internally with the company, then sometimes I use formatting - knowing my recipient is equipped with the necessary applications to read it.
-Frank