It's the server which needs to recognize your password. Thunderbird is only the messenger, and is not checking your password by any means.

Who is your email provider?

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

The server recognizes the password when I log onto it from my desktop. The server recognizes the password when I log onto it from my cell phone. The only thing that doesn't work is when I ask Thunderbird to access the server. Charter.net is my email provider. Here is my troubleshooting info from the clipboard:

 Application Basics

   Name: Thunderbird
   Version: 52.2.1
   User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20170622064432
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

 Mail and News Accounts
   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account5:
     INCOMING: account5, , (imap) mobile.charter.net:993, SSL, passwordCleartext
     OUTGOING: , mobile.charter.net:587, SSL, passwordCleartext, true

 Crash Reports

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 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.13.1
     4.13.1

     NSS
     3.28.5
     3.28.5

     NSS Util
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     3.28.5

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     NSS S/MIME
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In Account Settings > Server Settings Is 'User Name' = full email address eg: name at charter dot net ? make sure there are no hidden but additional blank space at the end or typos.

Check what is saved in thunderbird: 'Menu icon' > 'Options' > 'Options' > 'Security' > 'Password' tab click on 'Saved Passwords' button click on 'Show passwords' button You should see two lines one for imap and one for smtp double check the user name and the password. right click on a line and select eg: 'Edit Password' to modify an entry. click on Close click on OK

I presume a pop up asks for password, after entering password, select the checkbox to remember password. assuming it does not work.... What error message do you get...word for word?

Full email address is entered correctly whether I type it in one character at a time or paste it from an external source.

The correct password is stored in the saved passwords security page.

I get error messages in pop up boxes that say: Mail Server Password Required, and there's a box to enter my password.

When I enter the password, I get another box that says: Login Failed, and I'm allowed to Retry, Enter New Password, or Cancel.

Retrying and entering the password again fails again.

This is the same password my cell phone uses to check my email and I use when logging onto the ISP. It was Charter, but it's now Spectrum. I've been assured by their customer service people that the login is still charter.net, not spectrum.net.

You can try to see if this or this question is of help (ignore the POP related part).

Did you actually remove the stored password from Thunderbird first?

I've done all this many times. I'm connected to my router by cable since it's a desktop computer. I've uninstalled Thunderbird then reinstalled the latest version. I'm now giving up on Thunderbird after using it for over 20 years. I can go straight to Charter. Is there a way to export my address book so I can get it into Charter?

Sorry, I can’t help with that, but will admit it would be a waste to see a long-time Thunderbird user abandoning it for this reason, which is apparently what Charter wants. If someone (temporarily) changes the road to my house that I’d followed for 10 years or more, I would not even consider exchanging my car that I’ve been happy with because it’s too wide too fit that road, while I know there is nothing wrong with my car because I didn’t modify it. ;)

I’m not familiar with Charter but have seen quite a number of issues with them (as with other clients), and most users tend to either abandon Charter or at least their email service rather than leaving Thunderbird. Besides, you don’t have to switch - you can have several clients installed and use them all, especially with IMAP. That would also be useful to find out whether an issue is temporary, server or client related, as would trying another profile (reinstalling does rarely solve issues, as te same settings will be applied.) And of course, Charter is migrating, so it seems obvious where the issue originates.

Your issue is a tiny one, and could be fixed within minutes by either:

- creating a new profile and see if you can set up the account there - removing the stored password(s) as suggested, restarting Thunderbird and re-entering the password when asked - changing the connection security to None - changing the password type to Normal password - making sure both the IMAP and SMTP servers configured in Thunderbird have similar connection methods and password types - find out if Charter wants you to use an app password and use that (I couldn’t find that info) - enabling logging for IMAP to see what the server says.

And of course, solving this may help other users as well as developers in case Thunderbird has an issue.

I've been with Charter since they bought Cablevision in my area many years ago; so long in fact that I could only have eight letters in my email address name. I have no reason to be partial to them other than they have given me exceptional service the whole time. Their customer service people have tried everything they can to help me on this. But the cold, hard facts are: - logging in one morning the same way I have for years didn't work - Thunderbird keeps asking for my charter.net pw but won't accept it - I can log in to charter with my current password - my phone can log in with my current password

I have done the first five things on you list with no success. I've not only created a new profile, I've uninstalled and reinstalled Thunderbird from scratch. I don't know what using an app password means, but I'll ask charter. I don'y know what enabling logging for IMAP means. However, I infrequently get a message that says "Mail server (my name)@charter.net is not an IMAP4 mail server.

I don't like Outlook. I'm going to find another client to try. That should help determine my direction from there. I'm also going to change my Charter password to something simple and see what happens.

I fully understand, and am not saying you should abandon them. However, being bound to their email service is another thing. You could for instance consider switching your email only to a "known and stable provider" (and that doesn’t need to be Gmail.) For instance, I used about 3 or 4 providers for connectivity ever since accessing the net, but always used 1 email provider (that several other email accounts forward to, if I even use the ISP’s email, or others), which also allows me to switch ISP’s when I want without the hassling of changing email setups.

Additionally, in telco land, it’s not uncommon for helpdesk people to be unaware of some changes in that telco’s network, let alone clients getting affected, or they even do know (or are eager to help you out) but are simply instructed not to because doing so has no top priority, all of a sudden involves so-called "unsupported software", or some guy in the company dislikes Mozilla software for some reason. And of course, there are side effects during platform migrations (believe me, I’ve been there.) In my opninion, the best ISP’s are the ones providing a solution in that case, as well as proper instructions for users which are easy to find afterwards.

For your issue:

"- logging in one morning the same way I have for years didn't work"
-> proves there may be nothing wrong with your Thunderbird, other than that it could have been updated (check its Update History in Options > Advanced panel > Update tab), or any security related software updated (same for that software), or one of its features. If you would have a second PC with Thunderbird, you might be able to tell whether the issue is system related.

"- Thunderbird keeps asking for my charter.net pw but won't accept it"
-> That’s clear, but it didn’t for years, so it shouldn’t now, and most likely, nothing has changed in your setup. I’ve never seen Thunderbird changing passwords by itself and ask for it again the way it does now because it simply lost it, was unable to store it, or Thunderbird corrupting. Security software would be more likely to interfere, and even Windows 10 updates do strange things lately.

"- I can log in to charter with my current password"
-> Of course, since there is nothing wrong with your password. Unless an ISP suddenly requires you to use an app password for specific applications ,or starts using OAuth2 for logging in.

"- my phone can log in with my current password"
-> Most likely because a) your phone has another connection than Thunderbird (unless it’s over WiFi, but presumably uses the phone company’s network), or/and b) your phone does not use Thunderbird

Thanks you for trying the suggestions.

For reinstalling: in most cases ( I think 90%), reinstalling Thunderbird or Firefox does not solve an issue as settings are stored in their profile. But there are cases where it does help, so you could safely try without losing your email and settigs.

For the new profile (and for reference): I rely on the user to also use (launch) TB with the new profile, not only creating it (i.e. be sure to choose it).

App passwords are additional passwords that many email providers have started using lately as a security step. Thunderbird is known to not display a dialog when prompted for it, or one should create one at the ISP’s end and enter that instead of the usual password. (To be honest, I have never needed to use one so my knwoledge on that is limited.)

Enabling logging can be used for debugging, so that a user can actually see what the server and client say to each other, including the actual error and its cause. It may look a bit technical but is actually not much work to set it up. I recently did - you could use the content below and paste it into a file (e.g. tbtest.bat) and run it instead of the usual Thunderbird shortcut: set MOZ_LOG=IMAP:5,timestamp set MOZ_LOG_FILE=%USERPROFILE%\Desktop\imap.log pause "%ProgramFiles(x86)%\Mozilla Thunderbird\thunderbird.exe" This will create a log file on your desktop that can actually get very large if you run Thunderbird for a long time, but it would be good enough to know what happens during email retrieval. That means you can quit Thunderbird after a few attempts and restart it like you would normally do, so the log file won’t get that big. This may be the best option to see what happens, so perhaps you can try that and post the logged part here?

If you decide not to stick with Thunderbird (and I presume that would be because you don’t like it either), that’s your choice. Feel free to add another client or use webmail for the time being or as a test, or permanently. Unfortunately I’m unable to add a Charter email account myself, or I would definitely do so to see what the server says, also by logging.

Changing the password from Charter wouldn’t be a bad idea at all - it would force Thunderbird to apply other settings. That’s why I asked if you actually removed the password. Thunderbird may have an issue or need to get some change implemented, as it also did a while ago by this bug for instance.

Perhaps the only advice left that I can give is to disable any security software, reboot (or reboot Windows with networking enabled) and retry to see if it connects. Given that you mentioned the "<server> is not a valid IMAP4 server" info, that lead me to this page, also mentioning firewall/security software. Perhaps some feature in that was enabled or implemented recently?

_{/edit: changed program folder path for logging}

I installed another email client, and the same thing is happening. That means it's not in Thunderbird. That makes me happy. So now I get to wake up the Charter people.

Can you confirm that you have: Exited thunderbird. Accessed your Firewall, which may be part of an Anti-Virus Product, and set Thunderbird to be allowed. If it says it is allowed, then select to block and ok it and then access again and set to 'allowed'. Then start up Thunderbird.

How can I rebuild my Thunderbird profile? Or can I delete it, I know where it is, and reinstall Thunderbird? Would that let me enter correct data in the profile?

How can I rebuild my Thunderbird profile?

What do you mean with 'rebuild'?

Or can I delete it, I know where it is

I don't think anyone can prevent you from doing this. But what are you trying to achieve in the first place?

Or can I ... reinstall Thunderbird?

You can do that as many times as you want, but it won't do you any good. It won't change a thing on the profile, so you'd just waste your time.

If you want to start from scratch, create a new profile. https://support.mozilla.org/kb/using-multiple-profiles

PoppoJohn said

How can I rebuild my Thunderbird profile? Or can I delete it, I know where it is, and reinstall Thunderbird? Would that let me enter correct data in the profile?

It sounds like somebody told you to do so, or...? ;-) Unless you thought you had created a new profile by saying

I've not only created a new profile, I've uninstalled and reinstalled Thunderbird from scratch.

...assuming a reinstall does that (or "rebuilds" it) for you. It does not - a profile is the collection of user files associated to all your email and the accounts set up, and other settings for Thunderbird.

However, you know the issue is probably not with Thunderbird. Given that, I would first disable any firewall/security product or even uninstall it entirely and reboot Windows, or just start Windows in Safe Mode with networking enabled and see if the issue persists.

If that still fails, you should create an additional profile as (also) suggested earlier, be sure to choose that when starting Thunderbird, and set up the account there, as a test.

See https://support.mozilla.org/en-US/questions/1172043

I've created new profiles. I've booted Win 10 into safe mode with networking. Nothing works. I'm going to have to go back to my ISP for the umpteenth time and give them another chance to fix it.