How can I change an IMAP server on an existing T-bird account after T-bird deleted the saved password and IMAP server for that account?

- Who is your email provider?

- How do you authenticate, by OAuth2 or be Normal Password?

Do you want to actually CHANGE the server information, or just return it to what it once was? If the latter, plugging the old information won't affect your already-downloaded messages.

I don't know for sure if changing an account's IMAP server name to something different will retain your already-downloaded messages. I "think" it won't, but I'm not in a position to test that. It would be wise to make a safety backup copy of your Thunderbird profile before doing so, just in case. Actually, you should make regular backups of your Profile if your email is valuable to you

You can change the IMAP server name and settings in <Account Settings | Server Settings>. This may trigger your email provider to ask you to re-authenticate. It's easiest to delete any Saved Passwords for that account in <Settings | Privacy & Security | Passwords | Saved Passwords>. Then restart Thunderbird, and you should be asked for your credentials.

If you use OAuth2, a browser window will open where you can enter your user ID and password. You must have cookies allowed in Thunderbird for this to work. If you use Normal Password, depending on your provider, you may need to create and use an "application password", which would be distinct from your regular log-in password.

Hi, Lin: Thank you for your reply. My E-mail provider/ ISP is AT&T (Yahoo), meaning that it runs on Yahoo's platform, but AT&T does its own modifications to it. My authentication for T-bird is by "Normal Password," but for AT&T that means getting from AT&T a "Secure Mail Key" (SMK) to act as T-bird's password, which I have done before, and can do again.

I had tried to change the IMAP server name by adding "export." to the front of the normal one (imap.mail.att.net). This was recommended by several users of a Reddit forum, as an attempt to bypass the 10,000 max. messages usable in the T-bird Inbox instituted in 2022 by Yahoo. One of those users said that worked last October. But my doing so caused AT&T and/or T-bird to DELETE the IMAP server and password (SMK) from the "Saved Passwords" table in T-bird's "Tools -> Options -> Privacy & Security -> Passwords. It kept the SMTP server and its password in the table. Now I can't figure out how to add back the IMAP server name and password into the table. AT&T's article "Create a secure mail key" ( https://www.att.com/support/article/email-support/KM1240308/ ) says (as final step 5.), "For an IMAP account, delete the existing password for both the IMAP and SMTP servers. Replace them with your secure mail key." I can do that, but this is different from their requirement the last time I did it, when they required a different SMK for each of the IMAP server and the SMTP server. I was going to try the Reddit forum-recommended "export.imap.mail.att.net", to see if I could get the 67,000 messages in my AT&T Inbox into T-bird again, vs. the 10.000-message limit, but I would settle for just getting back to the standard imap.mail.att.net IMAP server and having T-bird work again.

My guess is that I could try the "export." prepend without destroying the messages in T-bird, given that I tried it yesterday and the messages are still in T-bird. Even if it DOES destroy the messages in T-bird, I can download them again from AT&T -- it will just take another 6 hours. Coincidentally, BEFORE I tried ANY of this stuff yesterday, I decided to check E-mail on T-bird at ~2:00pm CDT. I first checked my secondary AT&T E-mail address, and it acted fine. But when I clicked on my primary AT&T address, T-bird seemed to spaz and not be ABLE to update. T-bird gave an error message: "Server doesn't respond -- server says 'Server ERROR' -- Try again later." T-bird appeared to LOSE folders I clicked on, then lost them ALL! I closed T-bird, and started it again ~3:00pm CDT. With the secondary AT&T E-mail address OK, clicking on my primary AT&T address showed NOTHING in it, so T-bird proceeded to re-download the entire mess from AT&T's server again! First was the most recent 10,000 messages in the Inbox, followed by the Sent box. T-bird re-created the other folders I had on the server, and downloaded all of those ~15,000 messages to those folders too, all at about 2 messages per second,, over about 6 hours.

As for "RE-authentication" after a change to the IMAP server address, AT&T (through T-bird) wanted my user name (E-mail address) and password yesterday after I changed the IMAP server, but when I entered my standard (type-in) password, it didn't work, which I assume means that it wanted a NEW SMK instead, which I didn't have. If I go get a new SMK from ATT.com, and type that into the requested line, I imagine it will probably work -- then, but every time thereafter it will probably ask me again for the new SMK. So how can I get the new SMK and the new IMAP server into the Saved Passwords table again for AUTO-authentication?

As for making a safety backup copy of my Thunderbird "profile," I'm not sure what you mean by "profile." Is that the entire content of T-bird with all the messages, or some set of files with just the Settings and where T-bird left off with the last download for each E-mail account?

Also, in my on-line search for how to bypass the problem of the 10,000-message limit for the Inbox kept in T-bird (or Outlook or other E-mail clients) instituted by Yahoo in 2022, I noticed that all the complaints about that were in the summer of 2022. I also saw that the folks in charge of the IMAP protocol had proposed new functions & code which E-mail client companies could implement which would bypass the 10,000-message Inbox limit, using a new group of UIDONLY commands. I don't know if that ever got formally adopted, or whether Mozilla implemented it for T-bird, but it's possible. So maybe upgrading my T-bird v.78.7.0 (Jan. 26, 2021) to a later version (after 2022) would incorporate such possible changes in T-bird. I just thought that I might get T-bird working again for my primary AT&T E-mail address before I tried a T-bird upgrade.

Thank you in advance for any comments and/or suggestions you have on the above.

I can't use the trendy phrase TLDR (Too Long Didn't Read), but you're very verbose and I'm having trouble picking the essential issues out of your post. But I'll make some comments:

- According to this support article <https://help.yahoo.com/kb/SLN37064.html>, basic Yahoo service has a storage size limit of 20 GB, regardless of how many messages there are. You can pay extra for more space.

- Thunderbird has no practical limit on number or size of messages or folders. The only limits are those imposed by the email provider, and possibly local file system limits in older operating systems.

- If you're running up against Yahoo's limit, rather than relying on some unsupported hack like the "export" thing, maybe you should consider alternatives like transferring some of those messages to a second account. Or moving some messages to Local Folders in Thunderbird, thus taking some pressure off your Yahoo/ATT account. The only reason to keep all those thousands of messages on the server is so they are always accessible on multiple devices. That would be a valid reason, of course, but it is really necessary for you?

- Your Thunderbird Profile is where all your messages, folders, preferences, filters, passwords, etc. are stored. It's separate and distinct from the actual program. You can find its location by going to <Help | Troubleshooting Information | Profiles | about:profiles | Default Profile | Root Directory>. Clicking the Open Folder button will open your operating system's file browser in your Profile folder. In Windows, the default location is:

"C:\Users\(Windows account)\AppData\Roaming\Thunderbird\Profiles\(Thunderbird Profile)"

You can make a backup copy of this folder (while Thunderbird is closed) and restore it if ever something goes wrong. Actually, you should make regular backups of this folder if your email is precious to you.