Since a few weeks my first attempt to send an email to the mailing list always fails:

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host mailstore1.secureserver.net [72.167.238.29] said: 
<ae-list@media-motion.tv> recipient rejected
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When I send the same message a few seconds later again, it gets accepted immediately.

Any ideas what goes wrong? Someone else having the same issue?

Cheers,
Mathias