[Evolution] Failed to send: relaying denied

[Carr Wilkerson <cwilkers tulane edu>]

When trying to send email with evolution, I am getting the following
message. I'm not sure what I could have done to cause this, but it was
working fine previously.


-----------------------------------
Error while performing operation:
RCPT TP <email address here> failed: <email address here>... Relaying
denied. Proper authentication required.
-----------------------------------

where email address here is the 'TO' email address of the recipient. 
The message is not sent. Any clue?

Thanks.