Suggest you try this: Archive older sent emails.

If you set up Archive options to monthly, and retain folder structure, those emails will easily be located. This will reduce the file size of the Sent Folder.

Archive options:

• https://support.mozilla.org/en-US/kb/archived-messages
• http://kb.mozillazine.org/Archiving_your_e-mail

check your 'Sent' folder location:

• 'Tools' > 'Account Settings '> 'Copies & Folders' for the account
• select: 'Place a copy in'

If standard Pop mail account:

• select 'Sent' folder on' and account name

If IMAP mail account and you want emails kept on server:

• select: 'Other' and 'Sent on mail account'

If IMAP mail account and you want emails kept on computer:

• select: 'Other' and 'Sent on Local Folders'

click on OK to save changes

I just started using Firefox, so there are no messages in sent folder to archive.

I think you mean have just started using 'Thunderbird'email client, as 'Firefox' is a browser  :)

Please tell me exactly what settings are currently being used as per info in my previous response...check your 'Sent' folder location:

Do you have a Pop or an IMAP mail account ?

Do you have a gmail account?

If a Pop mail account is it using it's own mail account and folders or is it set up as a Global Account to use the Global Inbox (Local Folders)

It is odd, but the incoming uses IMAP while the outgoing uses SMTP. The server name is the same for both. Other accounts have unique names for sending and receiving.

Please post this info:

In Thunderbird

• Help > Troubleshooting Information
• click on 'Copy text to clipboard'
• then paste the info into this question.

You can edit / remove all info on fonts and printers, but nothing else.

Tell me which account number is having the problem.

It is listed as account3 that I am having the send folder problem with.

 WARNING:
 This contains sensitive information which shouldn't be forwarded or published without permission.

 Application Basics

   Name: Thunderbird
   Version: 24.5.0
   User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0
   Profile Folder: C:\Users\Donald\AppData\Roaming\Thunderbird\Profiles\sp9vvlxf.default
             (Local drive)
   Application Build ID: 20140424091057
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Crash Reports: about:crashes
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, [email protected], (imap) imap-mail.outlook.com:993, SSL, passwordCleartext
     OUTGOING: smtp-mail.outlook.com:587, alwaysSTARTTLS, passwordCleartext, true

   account2:
     INCOMING: account2, Local Folders, (none) Local Folders, plain, passwordCleartext

   account3:
     INCOMING: account3, [email protected], (imap) secure.emailsrve.com:993, SSL, passwordCleartext
     OUTGOING: smtp.reagan.com:587, alwaysSTARTTLS, passwordCleartext, true

   account4:
     INCOMING: account4, Microsoft Communities, (nntp) msnews.microsoft.com:119, plain, passwordCleartext
     OUTGOING: smtp.reagan.com:587, alwaysSTARTTLS, passwordCleartext, true

   account5:
     INCOMING: account5, [email protected], (imap) imap.googlemail.com:993, SSL, passwordCleartext
     OUTGOING: smtp.googlemail.com:465, SSL, passwordCleartext, true

 Extensions

 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: 24.5.0
     font.internaluseonly.changed: false
     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.enable: true
     mail.winsearch.firstRunDone: true
     mail.winsearch.global_reindex_time: 1399299451
     mailnews.database.global.datastore.id: 5cf7637c-2290-42c2-afaa-fb462254716
     network.cookie.prefsMigrated: true
     places.database.lastMaintenance: 1399305127
     places.history.expiration.transient_current_max_pages: 100646
     plugin.importedState: true

 Graphics

     Adapter Description: ATI Radeon 3000 Graphics (Microsoft Corporation - WDDM v1.1)
     Vendor ID: 0x1002
     Device ID: 0x9616
     Adapter RAM: 256
     Adapter Drivers: aticfx64 aticfx64 aticfx32 aticfx32 atiumd64 atidxx64 atiumdag atidxx32 atiumdva atiumd6a atitmm64
     Driver Version: 8.97.10.6
     Driver Date: 6-20-2012
     Direct2D Enabled: false
     DirectWrite Enabled: false (6.3.9600.16384)
     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: 1
   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've located this info which I think is what you need: http://www.rackspace.com/apps/support/portal/1088

Change your Account Settings > Server Settings for mail account

Incoming IMAP with SSL:

• server name: secure.emailsrvr.com (Note the spelling and edit)
• port: 993
• connection security: SSL
• Authentication Method: Password

Create this Outgoing SMTP server and then make sure the mail account settings use it.

Outgoing SMTP with SSL:

• server name: secure.emailsrvr.com
• port: 465
• connection security: SSL
• Authentication Method: Password

Thank you. Spelling things correctly helped. I sent a message, and it eventually showed up in the "Sent" folder. Thank you for the time and research you put into this for me.