In order for us to better investigate this issue you need to add a little more non-personal information.

Please add the troubleshooting information to your post To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

Application Basics

   Name: Thunderbird
   Version: 38.5.1
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20151228123010
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (pop3) pop.mail.yahoo.com:995, SSL, passwordCleartext
     OUTGOING: smtp.mail.yahoo.com:465, SSL, passwordCleartext, true

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

 Crash Reports

 Extensions
   Lightning, 4.0.5.2, false, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   McAfee Anti-Spam Thunderbird Extension, 2.0, false, msktbird@mcafee.com

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
     browser.cache.disk.smart_size_cached_value: 358400
     browser.cache.disk.smart_size.first_run: false
     browser.cache.disk.smart_size.use_old_max: false
     extensions.lastAppVersion: 38.5.1
     font.name.monospace.el: 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.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.x-cyrillic: Cambria
     font.name.serif.x-unicode: Cambria
     font.name.serif.x-western: Cambria
     font.size.fixed.el: 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.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: 02231691-fae7-4367-ae71-773a9a49d52
     network.cookie.cookieBehavior: 2
     network.cookie.lifetimePolicy: 2
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1459975264
     places.history.enabled: false
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true
     privacy.donottrackheader.enabled: true

 Graphics

     Adapter Description: Intel(R) HD Graphics 4400
     Vendor ID: 0x8086
     Device ID: 0x041e
     Adapter RAM: Unknown
     Adapter Drivers: igdumdim64 igd10iumd64 igd10iumd64 igdumdim32 igd10iumd32 igd10iumd32
     Driver Version: 10.18.10.3412
     Driver Date: 1-29-2014
     Direct2D Enabled: false
     DirectWrite Enabled: false (6.2.9200.17568)
     ClearType Parameters: ClearType parameters not found
     WebGL Renderer: false
     GPU Accelerated Windows: 0

     AzureCanvasBackend: skia
     AzureSkiaAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: cairo

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.10.10
     4.10.10

     NSS
     3.19.2.1 Basic ECC
     3.19.2.1 Basic ECC

     NSS Util
     3.19.2.1
     3.19.2.1

     NSS SSL
     3.19.2.1 Basic ECC
     3.19.2.1 Basic ECC

     NSS S/MIME
     3.19.2.1 Basic ECC
     3.19.2.1 Basic ECC

I hope this is the info you were asking for. Thanks!

Yep, thank you.

Your account uses POP which means it can only see the Inbox. To see the other folders you mention, you would need to set up the account to connect using IMAP. My own yahoo-based accounts use IMAP, so I know it's possible.

I'm not sure any of this will help with the older messages, unless you have sorted them to different folders?

Thank you - I will make the change and see what I can do about the folders. The older messages are all in the inbox. I was wondering if there is a setting I can change that will let it pick up mail older than 1/1/14?

Thanks for your help!

In general, the client downloads what is offered by the server. I'd expect any limit (by date, for instance) to be a server function. I don't know of any settings in Thunderbird to either allow or prevent old messages to be collected.

Thanks for all your help!