
5th February 2013, 20:09
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Super Moderator
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Join Date: Apr 2005
Location: Lüneburg, Germany
Posts: 41,685
Thanks: 1,899
Thanked 2,599 Times in 2,448 Posts
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Maybe those external servers blacklisted your mail server. It is possible that they were configured to reply with a (misleading) 500 error.
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