Please post the following info so the forum can understand the current setup.

In Thunderbird

• Open 'Help' (or click on three-line-icon and select Help)
• Choose 'Troubleshooting Information'
• Do not select check box "Include account names"!
• click on 'Copy to clipboard' button to select all.
• Right click in this forum questions 'Post a Reply' text box and select 'Paste'

Remove all the info on fonts and printers as it is not required.

First, Thank You for attempting to help! I got it going today and was going to post up what I did for others when I saw your response.

TDS insisted it was a Thunderbird config problem. I agreed to pay their offsite team if they fixed it. They couldn't.

In short, I had to delete the email account with TDS and get a new one.

Details: I removed the NO2 account (the "bad" one), rebooted, and added it back in. Same problem. Removed both accounts, rebooted, added both. Same problem. Uninstalled Thunderbird, rebooted, added both. Same problem. When I clicked "Add Mail Account" the name was pre-populated with "NO2".  ?? Uninstalled Thunderbird, rebooted, added NO2 first. No luck. Repeated, after running a couple of registry checkers and rebooting. Same problem. Uninstalled Thunderbird, and backed up the registry. Removed all entries related to Thunderbird and Mozilla (I felt weren't risky ;-) Ran the registry checkers , rebooted, installed Thunderbird. It didn't know NO2 this time. But, the disconnect message popped up. Removed both. I logged onto TDS, deleted the NO2 account, created a new one, NO3. Added NO1 and NO3 to Thunderbird. Smiled.

FWIW- In the process, I noticed the Profiles>>mail.tds.net folder had a ??.msf file that was ~850KB instead of 2-20KB like the others. It had part of a months old message I am certain was deleted. There was a TDS Pop account in Profiles>????.default (I have never had one), but not in the Thunderbird Account Settings.

Below is what I have now -- ANY comments appreciated!

===================
Application Basics

   Name: Thunderbird
   Version: 52.4.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20171004092449
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

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

   account4:
     INCOMING: account4, , (imap) mail.tds.net:993, SSL, passwordCleartext
     OUTGOING: , mail.tds.net:587, alwaysSTARTTLS, passwordCleartext, true

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

 Crash Reports

 Extensions
   Lightning, 5.4.4, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   Manually sort folders, 1.1.1, true, tbsortfolders@xulforum.org

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
     browser.cache.disk.filesystem_reported: 1
     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
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 52.4.0
     
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 2e319d09-8b8c-400b-b363-af7b6bf24b7
     media.gmp.storage.version.observed: 1
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1509229015
     places.history.expiration.transient_current_max_pages: 122334
     plugin.importedState: true
     security.sandbox.content.tempDirSuffix: {7d636fcd-61c9-46e7-a4d3-42438247bc7b}

 Graphics

     GPU #1
     Description: NVIDIA GeForce GTX 660
     Vendor ID: 0x10de
     Device ID: 0x11c0
     RAM: 2048
     Drivers: nvd3dumx,nvwgf2umx,nvwgf2umx nvd3dum,nvwgf2um,nvwgf2um
     Driver Version: 22.21.13.8205
     Driver Date: 5-1-2017

     Features
     Direct2D: false
     DirectWrite: true (6.2.9200.22164)
     WebGL Renderer: Google Inc. -- ANGLE (NVIDIA GeForce GTX 660 Direct3D9Ex vs_3_0 ps_3_0) -- OpenGL ES 2.0 (ANGLE 2.1.0.2a250c8a0e15)

     AzureCanvasBackend: skia
     AzureCanvasAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: skia

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.13.1
     4.13.1

     NSS
     3.28.6
     3.28.6

     NSS Util
     3.28.6
     3.28.6

     NSS SSL
     3.28.6
     3.28.6

     NSS S/MIME
     3.28.6
     3.28.6