unsubscribing problems

I would like to unsubscribe the mailing list ... for a week.

<procmail-request(_at_)informatik(_dot_)rwth-aachen(_dot_)de>: host
    relay3.rwth-aachen.de[134.130.3.4] said: 550 5.7.1
    <procmail-request(_at_)informatik(_dot_)rwth-aachen(_dot_)de>... Command 
rejected

What did I wrong ? :)

Greetings Thomas

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