OP wrote:
"I receive ok but cannot send. When I changed my Thunderbird settings to reflect the change to imap, all my Tbird folders and emails were gone."
First off, I'm going to suggest that if you try the following, you create the new account using Apple's Mail.app, and NOT with Thunderbird.
I believe that Comcast doesn't host its own email any longer.
They've "unloaded" that job over to Yahoo, and one now sends/receives "Comcast" emails through the Yahoo system.
(I could be wrong about this and what follows, I welcome correction from others)
What Mac you have, and what version of the OS becomes important here.
Older versions of the OS seem unable to authenticate properly with the Yahoo system.
I've run into this problem myself (which is what my info in this reply is based upon).
What Mac do you have (model and year made) and what version of the OS is running?
With a newer Mac and OS, I believe you need to do this:
- delete the existing account (assuming it's now "imap", your emails will remain on the comcast/yahoo server). OR... leave the existing account alone for now... you can delete it later.
- go to Settings and choose "Internet Accounts"
- click the "add account" button
- you can try selecting "yahoo", then creating a new account using your comcast email address and password. I can't remember if this works. But try it first.
If that doesn't work...
- GO BACK to the add account panel and this time choose "add other account". Again use your comcast email and password. See if it works this time.
If it's an OLDER Mac and OS, I believe that
the yahoo system now requires you to take an additional step for authentication.
This involves creating something called an "3rd party app password" that you enter during the account creation process (that takes the place of your "own" password). Again, my recollection here is nebulous, they don't really explain the process well.
In any case, you may need to go to this page:
If you use a 3rd-party email app to access your Yahoo Mail account, you may need a special code to give that app permission to access your Yahoo account. Learn how to create and delete app passwords.
help.yahoo.com
You create the 3rd party app password, and then save it (I recommend you save it into a "plain text" document created with Text Edit). Now you can file it somewhere safe for future reference.
Then you pretty much repeat the account creation process I described above, again using "other account", but this time replace "your" password with the 3rd party app password.
I believe that worked for me on my (other) older Mac with older software.
I hope this information proves of some use to you and again I apologize because I didn't keep records of exactly what steps I took.
Good luck.