First check that the password will get access to your webmail. If you are prompted to update the webmail password , then follow instructions. This happened to me and I had to update via webmail.

Then in Thunderbird, remove the stored password, both mailbox and smtp.

• Tools > Options > Security > Passwords tab
• click on 'Saved passwords'
• click on 'Show passwords'
• highlight the mailbox and smto passwords for account
• click on 'Remove'
• click on 'Close'

Restart Thunderbird. It should ask for password, enter at prompt and select Password Manager to remember the password. Click on OK.

I tried this already, I'm afraid...no luck. No harm in trying again, though...

tried again, no luck. But now there are no saved passwords displayed when I tried a third time.

What server settings are you using?

In Thunderbird Help > Troubleshooting Information do not select 'include account name' clickon 'Copy text to clipboard' paste info into this question you can remove all info on fonts and printers, but nothing else.

Application Basics

   Name: Thunderbird
   Version: 31.2.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20141012121702
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (none) Local Folders, plain, passwordCleartext

   account2:
     INCOMING: account2, , (rss) Feeds, plain, passwordCleartext

   account3:
     INCOMING: account3, , (pop3) popmail.dircon.co.uk:110, plain, passwordCleartext
     OUTGOING: smtp.talktalk.net:25, plain, passwordCleartext, true

   account4:
     INCOMING: account4, , (pop3) mail.dircon.co.uk:110, plain, passwordCleartext
     OUTGOING: smtp.dircon.co.uk:587, plain, passwordCleartext, true

 Crash Reports

 Extensions
   abcTajpu "a b c type-oo", 1.8.4, true, {15a7ef52-8a77-426e-9e17-e21af257d7c8}
   CompactHeader, 2.0.8, true, {58D4392A-842E-11DE-B51A-C7B855D89593}
   Display Quota, 0.3.7, true, {c1ac4523-76c2-9995-adbd-d93bf5141bea}
   ImportExportTools, 3.1, true, {3ed8cc52-86fc-4613-9026-c1ef969da4c3}
   Mail Summaries, 2.1.3, true, mailsummaries@mozillamessaging.com
   PrintingTools, 1.2.5, true, {5e9999c2-ba1d-44b6-bcee-5b30ce37d3b0}
   Signature Switch, 1.6.12, true, {2ab1b709-ba03-4361-abf9-c50b964ff75d}

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
     browser.cache.disk.smart_size.first_run: false
     browser.cache.disk.smart_size.use_old_max: false
     browser.cache.disk.smart_size_cached_value: 358400
     extensions.lastAppVersion: 31.2.0
     font.name.monospace.el: Consolas
     font.name.monospace.tr: Consolas
     font.name.monospace.x-baltic: Consolas
     font.name.monospace.x-central-euro: Consolas
     font.name.monospace.x-cyrillic: Consolas
     font.name.monospace.x-unicode: Consolas
     font.name.monospace.x-western: Consolas
     font.name.sans-serif.el: Calibri
     font.name.sans-serif.tr: Calibri
     font.name.sans-serif.x-baltic: Calibri
     font.name.sans-serif.x-central-euro: Calibri
     font.name.sans-serif.x-cyrillic: Calibri
     font.name.sans-serif.x-unicode: Calibri
     font.name.sans-serif.x-western: Calibri
     font.name.serif.el: Cambria
     font.name.serif.tr: Cambria
     font.name.serif.x-baltic: Cambria
     font.name.serif.x-central-euro: Cambria
     font.name.serif.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-western: Cambria
     font.size.fixed.el: 14
     font.size.fixed.tr: 14
     font.size.fixed.x-baltic: 14
     font.size.fixed.x-central-euro: 14
     font.size.fixed.x-cyrillic: 14
     font.size.fixed.x-unicode: 14
     font.size.fixed.x-western: 14
     font.size.variable.el: 17
     font.size.variable.tr: 17
     font.size.variable.x-baltic: 17
     font.size.variable.x-central-euro: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 17
     font.size.variable.x-western: 17
     gfx.direct3d.last_used_feature_level_idx: 1
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 33cbb87a-b8a6-4edb-878a-2b043e6c357
     network.cookie.prefsMigrated: true
     places.database.lastMaintenance: 1332493512
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true
     print.printer_Canon_iP4500_series.print_bgcolor: false
     print.printer_Canon_iP4500_series.print_bgimages: false
     print.printer_Canon_iP4500_series.print_colorspace:
     print.printer_Canon_iP4500_series.print_command:
     print.printer_Canon_iP4500_series.print_downloadfonts: false
     print.printer_Canon_iP4500_series.print_duplex: -856449972
     print.printer_Canon_iP4500_series.print_edge_bottom: 0
     print.printer_Canon_iP4500_series.print_edge_left: 0
     print.printer_Canon_iP4500_series.print_edge_right: 0
     print.printer_Canon_iP4500_series.print_edge_top: 0
     print.printer_Canon_iP4500_series.print_evenpages: true
     print.printer_Canon_iP4500_series.print_footercenter:
     print.printer_Canon_iP4500_series.print_footerleft: &PT
     print.printer_Canon_iP4500_series.print_footerright: &D
     print.printer_Canon_iP4500_series.print_headercenter:
     print.printer_Canon_iP4500_series.print_headerleft: &T
     print.printer_Canon_iP4500_series.print_headerright: &U
     print.printer_Canon_iP4500_series.print_in_color: true
     print.printer_Canon_iP4500_series.print_margin_bottom: 0.5
     print.printer_Canon_iP4500_series.print_margin_left: 0.5
     print.printer_Canon_iP4500_series.print_margin_right: 0.5
     print.printer_Canon_iP4500_series.print_margin_top: 0.5
     print.printer_Canon_iP4500_series.print_oddpages: true
     print.printer_Canon_iP4500_series.print_orientation: 0
     print.printer_Canon_iP4500_series.print_page_delay: 50
     print.printer_Canon_iP4500_series.print_paper_data: 9
     print.printer_Canon_iP4500_series.print_paper_height: 11.00
     print.printer_Canon_iP4500_series.print_paper_name:
     print.printer_Canon_iP4500_series.print_paper_size_type: 0
     print.printer_Canon_iP4500_series.print_paper_size_unit: 1
     print.printer_Canon_iP4500_series.print_paper_width: 8.50
     print.printer_Canon_iP4500_series.print_plex_name:
     print.printer_Canon_iP4500_series.print_resolution: 0
     print.printer_Canon_iP4500_series.print_resolution_name:
     print.printer_Canon_iP4500_series.print_reversed: false
     print.printer_Canon_iP4500_series.print_scaling: 1.00
     print.printer_Canon_iP4500_series.print_shrink_to_fit: true
     print.printer_Canon_iP4500_series.print_to_file: false
     print.printer_Canon_iP4500_series.print_unwriteable_margin_bottom: 0
     print.printer_Canon_iP4500_series.print_unwriteable_margin_left: 0
     print.printer_Canon_iP4500_series.print_unwriteable_margin_right: 0
     print.printer_Canon_iP4500_series.print_unwriteable_margin_top: 0

 Graphics

     Adapter Description: Intel(R) HD Graphics
     Vendor ID: 0x8086
     Device ID: 0x0042
     Adapter RAM: Unknown
     Adapter Drivers: igdumd64 igd10umd64 igdumdx32 igd10umd32
     Driver Version: 8.15.10.2827
     Driver Date: 7-31-2012
     Direct2D Enabled: true
     DirectWrite Enabled: true (6.2.9200.16571)
     ClearType Parameters: ClearType parameters not found
     WebGL Renderer: false
     GPU Accelerated Windows: 1/1 Direct3D 10

     AzureCanvasBackend: direct2d
     AzureSkiaAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: direct2d

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.10.6
     4.10.6

     NSS
     3.16.2.2 Basic ECC
     3.16.2.2 Basic ECC

     NSS Util
     3.16.2.2
     3.16.2.2

     NSS SSL
     3.16.2.2 Basic ECC
     3.16.2.2 Basic ECC

     NSS S/MIME
     3.16.2.2 Basic ECC
     3.16.2.2 Basic ECC

Can you offer some explanation.

The error message said : Mail server mail.btinternet.com responded: (#MBR1212) Incorrect username or password."

but you do not appear to have an account that connects to that server. eg:

  account3:
    INCOMING: account3, , (pop3) popmail.dircon.co.uk:110, plain, passwordCleartext
    OUTGOING: smtp.talktalk.net:25, plain, passwordCleartext, true

  account4:
    INCOMING: account4, , (pop3) mail.dircon.co.uk:110, plain, passwordCleartext
    OUTGOING: smtp.dircon.co.uk:587, plain, passwordCleartext, true

It's a mystery to me. I don't have a bt account. I just don't understand what's going on! Thanks very much for taking the time to look at this, it's much appreciated.

Do you have an email address that ends with @btinternet.com which talktalk allows you to use?

Tools > Account Settings > Outgoing Server or Menu Icon > Options > Account Settings > Outgoing Server

1. What smtp servers are listed? Please list all of them even if you are not using some.

2. select: smtp.talktalk.net click on 'Edit' button change port to 587 (as port 25 may cause issues.)

3. Is the 'User Name' your eg: talktalk.co.uk email address? What comes after the @ in the email address? Is User Name using the full email address or a part of it?

click on OK to save changes.

4. Have you ever had a btinternet.com email address and account or use btinternet.com as smtp server? If yes, did you ever edit the server info to change it to talktalk ? or did you just remove the account and create a new fresh one?

5. If you do not have mail.btinternet.com account, how did you remove the password for that account ? Are you saying that you have removed passwords for all your accounts ?

Can you get mail for account 3 or 4 or neither :

 account3:   (pop3) popmail.dircon.co.uk:
 account4:  (pop3) mail.dircon.co.uk:110, 

Can you send any emails from either account 3 or 4 or both ?

My first e-mail address, which I got about 20 years ago, was with a small company called Direct Connection (@dircon). This was taken over by Tiscali, and then talktalk. Talktalk is now my provider, but I've managed to keep the original dircon address, although this means that talktalk won't give me the full range of technical support. I have never had a BT address.

I can't edit the account - now when I click on Outgoing Server (SMTP) I get a message saying "An account with this name already exists. Please enter a different name".

I am becoming totally confused - I've never had a btinternet account...and what are accounts 3 and 4??