Returned mail from some email addresses

[Dave Mc]

The following message to <[email protected]> was undeliverable. The
reason for the problem: 5.1.0 - Unknown address error 550-'5.1.1 unknown or
illegal alias: [email protected]'

I get this message when I send to some email addresses but not all. I can
send to this email address from my earthlink web mail.

Thanks

 

[Vince Averello [MVP-Outlook]]

Is there any thing in common with the addresses that do or don't work?

 

[Dave Mc]

Not that I have noticed. I am going to try installing all Office updates and
see if that help.