e-mail kristensen wrong?

[GB:'X0B$4fAB92GB5]

Hi all
please can you tell mi why this is wrong?

 ----- The following addresses had delivery problems -----
<npkristensen at zmuc.ku.dk>  (unrecoverable error)

   ----- Transcript of session follows -----
... while talking to [130.225.206.2]:
>>> RCPT To:<npkristensen at zmuc.ku.dk>
<<< 550 Addressee unknown
550 <npkristensen at zmuc.ku.dk>... User unknown

Regards

Vratislav Richard Bejsak
Coleoptera - Australia, Tenebrionidae
Konevova 1658/110
130 00 Prague 3 Zizkov
CZECH Rep.
voice: (42+2) 270 849
fax  : (41+2) 311 6545
email: 76711,1261 at compuserve.com
(I am from Australia, this address is for one or two years)