Well, when you get the failure email, does the email address have a period on it? It should show the exact email address mail was sent to in the failure message
That would be too easy! If, for example, I send an email as described above, to an email address of firstname.lastname@example.org the failure email says this:
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
And the intended recipient does NOT receive any email. Would you do me a favor Gizmo, and try sending an email from your CP (using the method I described above) to an account for which you own the email address (create a test account if necessary) and see if it works for you? I'd like to know if this is a real bug or just happening to me.