Yahoo groups bouncing

[Kham Vue]

I'm using MS as relay and I'm getting a few bounced or 550 access denied
especially from yahoo groups.

Anyone got a clue why?

Here's my network:
[ router ] ---- [MS server] --- [firewall] --- [real mail server]

Here's my MX records:
        - outside: MX (20) ==> MS server, MX (50) ==> real mail server
        - inside: MX (20) ==> real mail server


---------- error msg --------------

----- The following addresses had permanent fatal errors -----
<rmendel at domain.com>

   ----- Transcript of session follows -----
... while talking to relay.domain.com.:
>>> MAIL From:<Exphys at aol.com>
<<< 550 5.0.0 Access denied
554 <rmendel at domain.com>... Service unavailable
-------------------------------------------

Kham Vue
Wadsworth Internet Service (WADSNET)
email: kvue at wadsnet.com
"Complex systems lead to complex problems."
- CAIB Report

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