not in list of allowed recipients????

[Trine Skj�l�s]

One of my customers receives an error message for some random recipients
saying"host not authorize domain name" and "the recipient is not in my list
of allowed ..."what is this?
I have no restrictions on our server. 


Trine Skj�l�s , Vika as , Strandgata 13 C, 2815 Gj�vik, Norway
[EMAIL PROTECTED] 
tlf :   +47 61 13 90 40 
fax : +47 61 13 90 41