looking for some help - just today i'm getting this message

Delivery to the following recipient failed permanently:



Technical details of permanent failu
PERM_FAILU SMTP Error (state 9): 553 sorry, that domain isn't in my
list of allowed rcpthosts (#5.7.1)

i get this sending from my blackberry and my macmail programs, so it's
not a common setting

could it be a problem on the recipients side?