In order to be able to find the correct solution to your problem, we require some more non-personal information from you. Please do the following:

• Click the application menu button at the top right of the toolbar, then click the Help menu and select Troubleshooting Information from the submenu. If you don't have an application menu, click the Help menu (alt+H) at the top and select Troubleshooting Information from the menu.

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Application Basics

   Name: Thunderbird
   Version: 24.4.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20140316131045
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Crash Reports: about:crashes
   Memory Use: about:memory

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

   account4:
     INCOMING: account4, , (imap) imap.mail.yahoo.com:993, SSL, passwordCleartext
     OUTGOING: smtp.mail.yahoo.com:465, SSL, passwordCleartext, true

 Extensions

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 1048576
     browser.cache.disk.smart_size.first_run: false
     browser.cache.disk.smart_size_cached_value: 1048576
     extensions.lastAppVersion: 24.4.0
     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
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: c37c2eb2-ef6f-4e7a-85ae-199faec25a8
     network.cookie.prefsMigrated: true
     places.database.lastMaintenance: 1396542287
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true

 Graphics

     Adapter Description: AMD RADEON HD 6450
     Vendor ID: 0x1002
     Device ID: 0x6779
     Adapter RAM: 1024
     Adapter Drivers: atiu9p64 atiuxp64 atiuxp64 atiu9pag atiuxpag atiuxpag atiumdva atiumd6a atitmm64
     Driver Version: 8.922.0.0
     Driver Date: 12-6-2011
     Direct2D Enabled: false
     DirectWrite Enabled: false (6.2.9200.16571)
     ClearType Parameters: ClearType parameters not found
     WebGL Renderer: false
     GPU Accelerated Windows: 0

     AzureCanvasBackend: skia
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: none

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.10.2
     4.10.2

     NSS
     3.15.4 Basic ECC
     3.15.4 Basic ECC

     NSS Util
     3.15.4
     3.15.4

     NSS SSL
     3.15.4 Basic ECC
     3.15.4 Basic ECC

     NSS S/MIME
     3.15.4 Basic ECC
     3.15.4 Basic ECC

I have this issue as well. It has been like this for a few days now.

Just found this link for a fix... http://forums.mozillazine.org/viewtopic.php?f=39&t=2817395&p=13453181

Per that Moderator "tanstaafl"

If you are getting a message that the login failed that implies you successfully made a smtp connection to a mail server. For debugging purposes it would be a good idea to delete the saved password in tools -> options -> security -> passwords and restart, to force it to prompt you for the password each time. That would also eliminate the possibility of your running into a known bug with saved passwords when Thunderbird has hard errors connecting to a mail server. Later on (when things work) you can click the checkbox in that popup to save the password.

Entering a Master Password for Thunderbird solved the problem although this is not a requirement. Perhaps a bug?

Thanks for the post