can you copy and paste the e-mail content with the unwanted "!" in it.
you could do a string replace on the unwanted chars, but it would also remove exclaimation marks that might be part of the content.
If the unwanted chars always show up in a specific fashion, you might be able to remove them witout affecting the desired ones.
Like if they looked like "!!!" you could replace them with:
$message = str_replace ("!!!","", $message);