Can you post your Troubleshooting Information?

AppMenu button - Help - Troubleshooting Information

Please also indicate which account is the one having problems.

The two accounts are: @aol.com and @netscape.net. I can't find which is 1 and which is 5. The netscape account is listed first on the left side of my main menu.

trouble shooting info:

 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
   account1:
     INCOMING: account1, , (imap) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: smtp.aol.com:587, alwaysSTARTTLS, passwordCleartext, true

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

   account5:
     INCOMING: account5, , (imap) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: smtp.aol.com:587, alwaysSTARTTLS, passwordCleartext, true

 Extensions
   Test Pilot for Thunderbird, 1.3.9, true, tbtestpilot@labs.mozilla.com

 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: 24.4.0
     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: 58f9ba94-a91b-40e1-9063-16a5ae0f9e9
     network.cookie.prefsMigrated: true
     places.database.lastMaintenance: 1395418389
     places.history.expiration.transient_current_max_pages: 104858
     places.history.expiration.transient_optimal_database_size: 167772160
     plugin.disable_full_page_plugin_for_types: application/pdf
     plugin.importedState: true

 Graphics

     Adapter Description: AMD RADEON HD 6450
     Vendor ID: 0x1002
     Device ID: 0x6779
     Adapter RAM: 1024
     Adapter Drivers: aticfx64 aticfx64 aticfx64 aticfx32 aticfx32 aticfx32 atiumd64 atidxx64 atidxx64 atiumdag atidxx32 atidxx32 atiumdva atiumd6a atitmm64
     Driver Version: 8.812.0.0
     Driver Date: 1-4-2011
     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

oops, forgot. The netscape account is the one having trouble.

Can you post the exact error message?

A Netscape email address basically is just an alias for an AOL account, so the SMTP server settings for both accounts are the same.

My best guess would be your Netscape email address got onto some sort of blacklist from AOL.

both accounts use the same outgoing server which I have set as the default. It is smtp.aol.com

An error occurred while sending mail. The mail server responded: 5.7.1 <jlminorusa@netscape.net>: Sender address rejected: not owned by user jlslmnr. Please check the message recipient jlslmnr@aol.com and try again.

First it asks for my password. I enter the aol.com password for the account above. (I deleted the other one). Then when I press retry, I get the message above.

I don't think it is AOL causing the problem for two reasons. First, I get incoming mail. Second, in all of my fooling around I happened to do something that let me send mail from netscape. I haven't been able to repeat whatever I did.

Do you have separate passwords for your Netscape and AOL accounts?
In that case you'll need to create two AOL SMTP servers, one for each account with the corresponding user id and password.

I think we are getting someplace. Do I need to set up new accounts? If so, can I save the present messages? I did have two separate passwords, but I deleted the netscape one. I've forgotten how and where I entered the passwords.

You do already have two accounts, so no need to set-up another one.

Go to your account settings:

AppMenu button - Options - Account Settings

Select 'Outgoing Server (SMTP)' at the bottom of the left pane.

What SMTP servers do you have?

You can also provide a screenshot.

http://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

I checked the two accounts and servers as you suggested. The first time it asked for my password, it said it was rejected. When I pressed retry, it was accepted and now everything seems to be working properly. Thanks so much to both of you. I really appreciate it.