It may help to post a screenshot of your SMTP server settings pane for possible feedback.

Response is at https://support.mozilla.org/en-US/questions/1513455 DO NOT respond here. This is a duplicate.

Attached is my SMTP server settings pane as suggested. Does this look correct?

Well, it looks proper to me. I compared to https://www.xfinity.com/support/articles/third-party-email-access Others on this forum may have other suggestions.

SMTP

Set Port to 587 Set Connection Security to : STARTTLS

Restart Thunderbird. Test sending.

Do you only have the one mail account email address that uses 'comcast' ?

Thank you Toad-Hall for your suggestions on changing my port and security settings. I changed these settings and restarted Thunderbird and restarted my computer. The changes did not fix the out going e-mail issue. Is anybody else having a similar outgoing e-mail issue or would there be any other changes I could try? Thank you in advance! Perhaps I should ditch Thunderbird and try a different third party e-mail software? Thank you also to David for your input on looking at my settings.

Your best bet is to stay here where support is offered. Problems with xfinity/comcast are common.

Here are a few checks you do: Firewall Access Firewall - it might be one supplied with computer or one you installed. Thunderbird must be set up as an allowed program.

Please confirm Thunderbird program is allowed. Q: What Anti-Virus product are you using ?

VPN Please check to see if a VPN has been enabled - some Anti-Virus products provide them. Basically, it hides your IP address so server does not like and thinks you are a hacker so it blocks access. Please switch off VPN.

Regarding IP address.... Switch off the router and wait for a good minute and switch it on again. This may establish a better IP connection which the server likes and is worth trying.

Check to see what password has been stored in Thunderbird.

• Settings > Privacy & Security
• scroll to Passwords section
• Clickon 'Saved Passwords'
• Click on 'Show Passwords'

If asked for a 'Windows Security' password - when you start up comuter and logon to your User Account - that is the password required. Look for the line that starts: smtp://comcast account details Is the 'Username' correct ?

• If no - right click on that smtp line and select 'Edit username' - completely clear contents and type in correct username.

Is password correct - either way I suggest you enter this again.

• right click on that smtp line and select 'Edit password' - completely clear contents and type in correct password.
• click on 'OK'

Then restart Thunderbird to ensure it is using the correct settings.

Additional stuff I located on the Xfinity customer forum - plenty of reports about not connecting to smtp server. Apparently, each Xfinity ID/email address must have a personal cell phone number or email address associated with it that is unique to the account to complete the password reset.

AS you changed the password - suggest you logon to webmail account and check you have the above set up.

One person found they had to wait 48 hours for password to get a proper reset: https://forums.xfinity.com/conversations/email/smtp-server-failure/6696d64f8c8da0745adcc6be

If the account settings are correct, start Windows in safe mode with networking enabled - https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode

Does problem change?

TRY CHECKING YOUR PASSWORD. After trying changing all the recommended settings, I checked my passwords in Settings -> Privacy & Security. There was a weird one dated today with OAuth. I deleted it. Then TBird asked for my password, which I keep on a spread sheet. Entered it and now it works fine.