The following recipient(s) cannot be reached:how do I allow

[Brendan]

The following recipient(s) cannot be reached:

'(e-mail address removed)' on 30/01/2009 20:36
553 sorry, that domain isn't in my list of allowed rcpthosts
(#5.7.1)

This is happening to most of my contacts

 

[F.H. Muffman]

The following recipient(s) cannot be reached:

'(e-mail address removed)' on 30/01/2009 20:36
553 sorry, that domain isn't in my list of allowed
rcpthosts
(#5.7.1)
This is happening to most of my contacts

Are the only ones that are working on the same ISP/Server as you? It sounds
like you need to authenticate with the SMTP server before you send messages.
What version of Outlook are you using?