Seriously, I doubt you are using imap. THe option to leave messages on the server until I delete them is not available on IMAP accounts.

So please add the troubleshooting information to your post that we might confirm which it is IMAP or POP among other things.

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.

I did as you requested. You are right, it was pop3, not IMAP as I initially thought.

 Application Basics

   Name: Thunderbird
   Version: 52.6.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20180123185941
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

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

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

   account3:
     INCOMING: account3, , (nntp) news.verizon.net:119, plain, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (pop3) pop.verizon.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, alwaysSTARTTLS, passwordCleartext, true

   account7:
     INCOMING: account7, , (pop3) mail37.pair.com:110, plain, passwordCleartext
     OUTGOING: , smtp.verizon.net:465, SSL, passwordCleartext, true

   account8:
     INCOMING: account8, , (imap) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.aol.com:587, alwaysSTARTTLS, passwordCleartext, true

   account9:
     INCOMING: account9, , (imap) imap.mail.yahoo.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.mail.yahoo.com:465, SSL, passwordCleartext, true

   account10:
     INCOMING: account10, , (imap) imap.gmail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

   account11:
     INCOMING: account11, , (imap) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.aol.com:587, alwaysSTARTTLS, passwordCleartext, true

 Crash Reports

 Extensions
   Lightning, 5.4.6, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}

 Important Modified Preferences

   Name: Value

     accessibility.typeaheadfind.flashBar: 0
     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
     browser.display.use_document_fonts: 0
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 52.6.0
     font.language.group: x-western
     font.minimum-size.x-western: 12
     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.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-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.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: 12
     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: 11
     gfx.blacklist.suggested-driver-version: 10.6
     gfx.direct3d.last_used_feature_level_idx: 0
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: a0d57aaf-be25-469e-93f9-a9b61e11cae
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"3"},"flaggedCol":{"visible":true,"ordinal":"7"},"attachmentCol":{"visible":false…
     media.gmp.storage.version.observed: 1
     network.cookie.cookieBehavior: 2
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1520790237
     places.history.enabled: false
     places.history.expiration.transient_current_max_pages: 122334
     plugin.importedState: true
     plugin.state.flash: 0
     print.print_printer: Net LJ4
     print.printer_Net_LJ4.print_bgcolor: false
     print.printer_Net_LJ4.print_bgimages: false
     print.printer_Net_LJ4.print_colorspace:
     print.printer_Net_LJ4.print_command:
     print.printer_Net_LJ4.print_downloadfonts: false
     print.printer_Net_LJ4.print_duplex: -121485024
     print.printer_Net_LJ4.print_edge_bottom: 0
     print.printer_Net_LJ4.print_edge_left: 0
     print.printer_Net_LJ4.print_edge_right: 0
     print.printer_Net_LJ4.print_edge_top: 0
     print.printer_Net_LJ4.print_evenpages: true
     print.printer_Net_LJ4.print_footercenter:
     print.printer_Net_LJ4.print_footerleft: &PT
     print.printer_Net_LJ4.print_footerright: &D
     print.printer_Net_LJ4.print_headercenter:
     print.printer_Net_LJ4.print_headerleft:
     print.printer_Net_LJ4.print_headerright:
     print.printer_Net_LJ4.print_in_color: true
     print.printer_Net_LJ4.print_margin_bottom: 0.5
     print.printer_Net_LJ4.print_margin_left: 0
     print.printer_Net_LJ4.print_margin_right: 0.300000011920929
     print.printer_Net_LJ4.print_margin_top: 0.5
     print.printer_Net_LJ4.print_oddpages: true
     print.printer_Net_LJ4.print_orientation: 0
     print.printer_Net_LJ4.print_page_delay: 50
     print.printer_Net_LJ4.print_pagedelay: 500
     print.printer_Net_LJ4.print_paper_data: -1
     print.printer_Net_LJ4.print_paper_height: 11.00
     print.printer_Net_LJ4.print_paper_name:
     print.printer_Net_LJ4.print_paper_size_type: 0
     print.printer_Net_LJ4.print_paper_size_unit: 0
     print.printer_Net_LJ4.print_paper_width: 8.50
     print.printer_Net_LJ4.print_plex_name:
     print.printer_Net_LJ4.print_resolution: 600
     print.printer_Net_LJ4.print_resolution_name:
     print.printer_Net_LJ4.print_reversed: false
     print.printer_Net_LJ4.print_scaling: 0.70
     print.printer_Net_LJ4.print_shrink_to_fit: false
     print.printer_Net_LJ4.print_to_file: false
     print.printer_Net_LJ4.print_unwriteable_margin_bottom: 0
     print.printer_Net_LJ4.print_unwriteable_margin_left: 0
     print.printer_Net_LJ4.print_unwriteable_margin_right: 0
     print.printer_Net_LJ4.print_unwriteable_margin_top: 0
     print.printer_NetLJ4.print_bgcolor: false
     print.printer_NetLJ4.print_bgimages: false
     print.printer_NetLJ4.print_command:
     print.printer_NetLJ4.print_downloadfonts: true
     print.printer_NetLJ4.print_evenpages: true
     print.printer_NetLJ4.print_footercenter:
     print.printer_NetLJ4.print_footerleft:
     print.printer_NetLJ4.print_footerright:
     print.printer_NetLJ4.print_headercenter:
     print.printer_NetLJ4.print_headerleft:
     print.printer_NetLJ4.print_headerright:
     print.printer_NetLJ4.print_in_color: true
     print.printer_NetLJ4.print_margin_bottom: 0.25
     print.printer_NetLJ4.print_margin_left: 0.5
     print.printer_NetLJ4.print_margin_right: 0.5
     print.printer_NetLJ4.print_margin_top: 0.25
     print.printer_NetLJ4.print_oddpages: true
     print.printer_NetLJ4.print_orientation: 0
     print.printer_NetLJ4.print_pagedelay: 500
     print.printer_NetLJ4.print_paper_data: 1
     print.printer_NetLJ4.print_paper_height: 11.00
     print.printer_NetLJ4.print_paper_size: 1768235124
     print.printer_NetLJ4.print_paper_size_type: 0
     print.printer_NetLJ4.print_paper_size_unit: 0
     print.printer_NetLJ4.print_paper_width: 8.50
     print.printer_NetLJ4.print_printer: NetLJ4
     print.printer_NetLJ4.print_reversed: false
     print.printer_NetLJ4.print_scaling: 1.00
     print.printer_NetLJ4.print_shrink_to_fit: true
     print.printer_NetLJ4.print_to_file: false
     security.sandbox.content.tempDirSuffix: {0930758f-f3ff-4ca4-86f6-d91bca022388}

 Graphics

     GPU #1
     Description: ATI Mobility Radeon HD 4650
     Vendor ID: 0x1002
     Device ID: 0x9480
     RAM: 1024
     Drivers: aticfx64 aticfx64 aticfx32 aticfx32 atiumd64 atidxx64 atiumdag atidxx32 atiumdva atiumd6a atitmm64
     Driver Version: 8.970.100.7000
     Driver Date: 11-16-2012

     Features
     Direct2D: false
     DirectWrite: true (6.2.9200.22164)
     WebGL Renderer: Google Inc. -- ANGLE (ATI Mobility Radeon HD 4650 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

It is account 1 that is having this problem. Most of the other accounts are inactive or essentially dormant. The file was too large to post intact. I deleted only the text that had to do with printer info for PDFCreator.

Lou57 said

It is account 1 that is having this problem. Most of the other accounts are inactive or essentially dormant. The file was too large to post intact. I deleted only the text that had to do with printer info for PDFCreator.

It is only rarely that the text after the account settings and extentions is of any use.

Now to your mail problem. Basically it will be an issue between the fundamental process used to work out which mail is downloaded and the cavalier way ISP's manage their mail systems these days.

When Thunderbird downloads mail and is instructed to leave messages on the server, it writes a log of what is what in a text file called popstate.dat. This file contains the reference number used by the server to describe the actual email.

This process works a treat, as long as the server operators respect the importance of these reference numbers. I am seeing more and more instances of providers not respecting that and re-indexing the mail on the server. To install new hardware or software or as some sort of maintenance I do not know. But it must also be remembered that when the POP protocol first appeared in the last millennium that having more that a couple of hundred emails in an account was bad form and would see you run out of space to store new incoming mail.

So what happens is the server re-indexes the mail, and all of the until I delete it and where and what was the last email stuff just goes up in virtual smoke. Thunderbird is forced to start getting your mail as it is it a new account as what it has stored is useless. The result is you get lots and lots of duplicates.

I think it may be germane that Verizon has migrated their email base to AOL.. That migration may have seen a re-index of mail. https://help.aol.com/articles/verizon-move-to-aol-mail-updating-your-third-party-email-program-or-mobile-device-with-your-new-account-information-pop3