[Exim] MX record not valid.

Hi,
If I send a mail to this address I get an error as follows:
--------------------------------------------------------------------------
This message was created automatically by mail delivery software.

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:

  courrier@???
    all relevant MX records point to non-existent hosts
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I checked the MX record (bind) on my server, and it's ok.
What does this mean ?
Is exim checking somewhere else ?

Thanks
Stveen