Font Size Changes from compose/send

When I compose a message in Windows mail, the font on my screen is bold and large (about 14). I did not set it that way, it just happened when I started the computer last week. When I send the message, the recipients complain that the font in almost microscopic (about 4). I have tried resetting the defaults etc in mail, but it doesn't seem to make a difference.
Can anyone help?

Thanks

Adanac