Short version: using e-mail ‘stetionery’ is evil. Don’t do it.
In my posting Leopard: The Good Stuff I say
One feature Mail could have done without: stationery. Stationery is terrificfor hand-written mail. All it does is add an image attachment that may or may not be seen as a “background” to the e-mail. (Many times it will not show upit depends on the e-mail client. The user will then click on the attachment to see it and it will make them wonder why you send them a fabric swatch.)
I have repeatedly suggested against it every time someone has mentioned it in the Apple discussion forums. I’ve written, “As I’ve stated before on these forums, just because it looks good in your e-mail client does not mean that it will display correctly in someone else’s. Sometimes the ‘stationery’ will be transmitted as an attachment. The recipient will get your e-mail and an attachment. They will have to click on the attachment to see it. And they will see the ‘stationery’ only. It would be like sending a postal letter with the words written on a plain white sheet of paper, and sending along with it a nice piece of colored stationery.”
A friend sent me e-mail the other day. He “signed his name” at the bottom with a GIF image of his handwritten name, “Joe.” It, was, of course, an attachment. It showed up fine in e-mail, but when I forwarded the message, I forwarded his plain text e-mail plus the attachment with his name.
Someone else consistently sends me e-mail with a fancy signature image, containing her company logo. Every time I reply—and include the e-mail—the fancy signature is sent along. She replies, and now there are two copies if it, and so on.
You, the sender, have no control over what the recipients’ e-mail client can and cannot view. Sticking to plain text e-mail means that you can communicate with the greatest number of people. If you must have fancy fonts, and colorful backgrounds, send it in a PDF.
Plain text is best.
Use Rich Text if you must.
But, don’t use stationery (unless it is in hard-copy, postal mail).