Please inspect the "encoding" attribute on the episerver.mail/sites/site/editor element of your EPiServerMail.config, I'm quite sure you'll find it to be set to "iso-8859-1".
When you say that you are using UTF-8, I assume that means you have encoding="utf-8" in EPiServerMail.config?
It is possible that the clients where the issue has been encountered simply do not support utf-8. Do you know of any examples of clients where the problem occurs?
Anyone know why certain recipients can't see ÅÄÖ in the mails I send from EPi Mail? All clients I've tested with (Outlook Exchange, Windows Mail and Gmail) can see the characters, but some users cannot, they're simply removed from the mail.
I'm using UTF-8. Thanks in advance.