millie,
For my Comcast accts, in SE Michigan I use Port: 465
So on my acct I use the following settings.

Click on Comcast acct under Mail Accts Press Properties button:
1. On the server tab I have;
a. Outgoing server: smtp.comcast.net
b. Check the box requiring authentication
c. Under Settings button I manually add my username and password
information in the text boxes provided. The other choice of "Use the same
settings as the Incoming server", won't work with my spam filter application
correctly.

2. On the advance tab I have:
a. For Outgoing server: Port: 465
b. Under Outgoing server the box to use SSL encryption checked.
c. For Incoming server:Port: 110
d. Under Incoming server the box to use SSL Encryption is not checked.
3. Press Apply to accept settings.

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"millie" wrote in message
...
I tried 587, got this error.........The message could not be sent
because the
server rejected the sender's e-mail address. Subject 'Test', Account:
'pop.mailcomcast.net', Server: 'smtp.comcast.net', Protocol: SMTP,
Server
Response: '550 5.1.0 Authentication required', Port: 587, Secure(SSL):
No,
Server Error: 550, Error Number: 0x800CCC78
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Millie
Tucson, AZ