Retrospect update 10.5.0 (145) appears to have fixed this issue for me.
In Retrospect for Mac 10.1, all backup operations (Mac, Windows, and Linux clients) return an "error -597 (mail server not found)" error. However, the E-mail test in my Retrospect preferences is always successful and I receive the test E-mail message every time. Very frustrating. Am I missing something? Anybody have any ideas?