Use alternative parts in your email with an HTML and a pure-text versions of your e-mail. People using mail clients that don't show HTML usually know how to rebuild the link from the pieces and won't blame the problem on you. The HTML version should protect the links.
and source code of both Tmail and ActionMailer when playing with mime like that...
here a little tip back, which I found in Rails Recipes.
I go for the multipart/alternative solution.
Sending an email as HTML AND Plaintext makes sense and is for me, the
way to go.
What helped me, to find a quick solution on changing the Action Mailer
behaviour in
Login Sugar, act_as_authenticated was this very helpful book
"Rails Recipes" look for the Recipe `Send Gracefully Degrading Rich-
Content Emails`.