Maybe the people who responded so far are misunderstanding the issue, or maybe they just don't have any help to offer. It's a pretty big deal, and it's a problem for me as well, so if anyone has any ideas, I would really appreciate them, and I'm sure OP would, too.
OP's and my issue is that emails sent from Windows Phone 8 embed 11 point Calibri for the entire email body via HTML style tags. This means that no matter what email client these emails are viewed in, the email body renders in 11 point Calibri, and there doesn't seem to be any way to change this.
Note that the issue is not which fonts are appropriate to use in a given setting. The issue is that emails I send from Windows Phone 8 are always displayed in 11 point Calibri.
This means that if someone is viewing an email sent from my Windows email in Gmail, which uses Arial as its default font, my email sticks out like a sore thumb. These emails even look different in the Outlook Web App because the default font there is not Calibri 11, either. It looks like I've chosen specifically to use Calibri, rather than just plain text, and it also renders quoted text in replies/forwards in Calibri as well.
It's disruptive and calls unwanted attention to the emails sent from my Windows Phone. Further, there's no way for me to send an email from my Windows Phone without everyone knowing I did so. This renders my Windows Phone useless for sending business emails, which is a big negative for a professional wanting to use WP as a primary device.
It seems ridiculous for WP to go out of its way to embed Calibri in the HTML, and it's even more ridiculous not to offer a way to change that. I hope I'm just missing something. Can anyone help?