No, it is a box you check.

Tools | Accounts | Mail | Properties | Servers. Is: My Server Requires
Authentication checked?

I don't know if this is the answer, just something to try since the error
message mentions it.

Your address is being rejected by Comcast. You may find some information
here as well.

Comcast FAQs:
http://www.comcast.net/help/faq/index.jsp?faq=Hot117481
--
Bruce Hagen
MS-MVP Outlook Express
Imperial Beach, CA


"Bob W" wrote in message
...
Thanks for response, Bruce.
I have already phoned Comcast and these were correct: POP3;
mail.comcast.net; smtp.comcast.net. Is that what is meant by
"authentication
checked"?
Bob

"Bruce Hagen" wrote:

Tools | Accounts | Mail | Properties | Servers. Is: My Server Requires
Authentication checked? The error message suggests that it should be.
--
Bruce Hagen
MS-MVP Outlook Express
Imperial Beach, CA


"Bob W" Bob wrote in message
...
Outlook Express has been used for a long time with no problems and nor
alterations have been made. 4 days ago the sent emails were rejected.
I
turned off computer over night and it worked again the next day. Then,
yesterday, the sent emails were rejected and I shut off computer
overnight.
Error problem still exists. Receiving emails works OK. I can send OK
through webmail at Comcast, but not from OE. Here is the Microsoft
error
message:

The message could not be sent because the server rejected the sender's
e-mail address. The sender's e-mail address was
'.
Subject 'testing', Account: 'Bob Wilmot', Server: 'smtp.comcast.net',
Protocol: SMTP, Server Response: '550 5.1.0 Authentication required',
Port:
25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC78