This article may help you. Yahoo requires a different password for email clients than for online. https://help.yahoo.com/kb/SLN15241.html

Thanks David, but I can't do that either. I tried for two hours yesterday and I cannot get to the page you listed. I am in an endless loop of signing in. I sign in and it goes to the Currently/Yahoo home page. I click Account info or Settings and go to the Settings page. I click on Account Security and it signs me out and asks me to sign in again. I deleted cache and cookies and turned off my virus protection. Still and endless loop of signing in. Frustrating. Thanks for trying. Shaw

I created a screenprint of that page for you. Attached.

I can get to that page. I follow the link in the first line. Then I go to Settings, etc (see previous note) and end up in a loop of sign in, log out every time I click on the Security tab on the left side of the page. Thanks for trying to help.

re :Mail server inbound.att.net responded: [SYS/TEMP] Server error - Please try again later."

That is a message from the server. It means there is a problem at the server end - not Thunderbird. As they mention the password has failed then it is possible you were using the normal password which you logon to see webmail account. Server does not like it.

But that error message says you are using the server: inbound.att.net not imap.mail.yahoo.com https://www.att.com/support/article/email-support/KM1010523/

Read this info and try the instructions to create secure mail key. Remember it needs to get set into both the imap and the smtp stored passwords in Thunderbird. https://www.att.com/support/article/email-support/KM1240308

Passwords stored: Menu icon > Preferences / Settings > Privacy & security click on 'Saved Passwords click on 'Show Passwords' Do the following for both the incoming and smtp for bellsouth email address/username: Right click on line and select 'Edit Password' Completely clear contents and enter the secure mail key. click on 'Done'

Exit Thunderbird, wait a few moments for background processes to complete and then restart Thunderbird.

Thanks Toad-Hall. I had some problems converting from POP to IMAP, but got the job done. The result is that I have a new account with all my email files in the old account. Thanks to you I have TB up and running again. Now I have to figure out how to move the old email files into the new account. Many thanks for the help. Shaw

When you put the emails into folders in the imap account, this means you are uploading them back onto the server. So, it will use a portion of your server quota.

However, please check the webmail account first. I'm not completely sure of the setup which the server uses, but as an example: Gmail keep all emails in the 'All Mail' folder. When you delete an email from a pop account Inbox, it only removes the 'Inbox' 'label'. So email is still on server in the 'All Mail' folder. This means if you logon to webmail, you can view 'All Mail' and put a copy back in Inbox - so email has an 'Inbox' label again thus it will auto reappear in the Inbox. When imap Inbox synchs with server Inbox the email magically reappears. This means you do not necessarilly need to upload the emails. So check to see if AT&T are using a similar method.

Otherwise - If email is in pop Inbox: Highlight a small batch of contiguous emails. Right click on highlighted batch of emails and use 'Copy to' and choose the relevant imap folder on imap account.

Select that imap folder which received the copied emails, to see if it contains the emails. Then logon to webmail account via a browser and check to see if all got uploaded ok.

Repeat the action to upload another batch of emails.

Please note there may be a limit on how much you can upload within a given time period.

The alternative is get all copies of emails from Pop into the Local Folders mail account. This means you can remove the pop account and still have access to all your pop emails. It will not use up any server quota. There is also a quick method of doing this via the profile folders. Basically you just copy all the mbox and *.sbd folders from the pop account name folder into the Local Folders folder. If you are interested in that approach let me know and I'll post more info on that process.

Please note: that an imap account cannot be considered as an independent copy of your emails because all imap folders synchronise with server folders. All emails are to that extent are stored on the server. You can download full copies and create a backup - let me know if you need more info on that topic.

Thanks Toad-Hall (I'm sure there's a good story about your handle!) All working now. I'm deleting all the emails I can before transitioning to imap. Many thanks.