SMTP Communications Probem

[Smithy10]

Usign 2003 Exchange server and I seem to get the following error message every now and again.


There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<domain name #5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)>

Any ideas as to why this happens. It does this for internal and external email addresses.
Thanks

 

[mattbedding]

Have had this many times (but only on external bound mail), and every time it was a problem with my ADSL provider who also provide SMTP service. So might be worth a call to check all their systems are ok.