problem with email access

Someone tries to sign on to a private game. The message is text/plain, the 
syntax seems to be ok but an error message is returned.

Any idea why? Any suggestion as to how to proceed?

Oskar

From the mail header:
-- begin --
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
To: [email protected]
Content-Transfer-Encoding: 8bit
-- end --

The error message
-- begin --
Incorrect password to modify player ID 'POWER#3'.
Unprocessed portion of message follows:
JOIN ...
--
[footer]
-- end --


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