Weird Email Problem

[J]

This just started happening today.

I can't send to a certain person's Earthlink address from one of my 
domain emails.  It keeps giving me the message about checking the 
configuration, the formation of the address, the smtp server, yadda 
yadda. Nothing was changed. I manually typed the person's address in. 
Still no soap.

Now a weirder thing has happened. I can't SEND from  one of my 
Earthlink addresses, so I deleted/recreated the account but still get 
that same message. What is causing this? It's just too weird.

I'm wondering if this one will even go, being that it's Earthlink as 
well.