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Matt, thanks for your help. Hope you see something here, but I'm not optimistic as I've looked at all the similar problems here. The IMAP account is the active one. I've left the POP account because she still has mail there, but the sending problem occurs with either account.

Ralph

 Application Basics

   Name: Thunderbird
   Version: 52.6.0
   User Agent: Mozilla/5.0 (Windows NT 10.0; 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, , (none) Local Folders, plain, passwordCleartext

   account3:
     INCOMING: account3, , (pop3) pop.east.cox.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.cox.net:465, SSL, passwordCleartext, true

   account5:
     INCOMING: account5, , (imap) imap.cox.net:993, SSL, passwordCleartext
     OUTGOING: , smtp.cox.net:465, SSL, passwordCleartext, true

 Crash Reports
   https://crash-stats.mozilla.com/report/index/bp-31f33e2e-25b9-42a5-bc02-3e6b50180301 (2/28/2018)
   https://crash-stats.mozilla.com/report/index/bp-03795fc6-655f-4117-9076-b09890180228 (2/28/2018)
   https://crash-stats.mozilla.com/report/index/bp-70bbe2c6-9012-4c39-8985-986332150301 (3/1/2015)

 Extensions

 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.zoom.full: true
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 52.6.0
     font.internaluseonly.changed: true
     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: Arial Black
     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
     gfx.blacklist.suggested-driver-version: 6.1400.1000.5218
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: ffd33e1b-3ce0-40af-be82-495c277c388
     media.gmp.storage.version.observed: 1
     network.cookie.cookieBehavior: 3
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1519582394
     places.history.expiration.transient_current_max_pages: 122334
     plugin.importedState: true
     plugin.state.npctrl: 0
     plugin.state.npgoogleupdate: 0
     plugin.state.npmcsnffpl: 0
     plugin.state.nppdf: 0
     plugins.update.notifyUser: true
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_bgcolor: false
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_bgimages: false
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_evenpages: true
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_footercenter:
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_footerleft: &PT
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_footerright: &D
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_headercenter:
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_headerleft: &T
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_headerright: &U
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_in_color: true
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_margin_bottom: 0.5
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_margin_left: 0.5
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_margin_right: 0.5
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_margin_top: 0.5
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_oddpages: true
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_orientation: 0
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_reversed: false
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_scaling: 1.00
     print.printer_\\GATEWAYCOMPUTER\HP_DeskJet_540-USB.print_shrink_to_fit: true
     privacy.sanitize.timeSpan: 0
     security.sandbox.content.tempDirSuffix: {5a359324-0638-4faa-abbc-c122535ee9eb}

 Graphics

     GPU #1
     Description: Intel(R) HD Graphics
     Vendor ID: 0x8086
     Device ID: 0x22b1
     RAM: Unknown
     Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32
     Driver Version: 20.19.15.4531
     Driver Date: 9-29-2016

     Features
     Direct2D: false
     DirectWrite: true (10.0.16299.15)
     WebGL Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics 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

Houston we have a problem.

Cox only offer encrypted connections. OR so their instructions would appear. https://www.cox.com/residential/support/imap-server-settings.html

However they only offer SSL V3 and TLS V1 encryption.

Thunderbird stopped accepting connection on those protocols more than a year ago because both protocols are broken and offer no security at all. The use of the protocols was abandoned as it is preferable to have no encryption and know you have none than toddle along thinking you have something that is broken.

What I would suggest in the first instance is change the connection security to none and try ports 587 and 465. Just to see if they will allow non encrypted connections despite what the web site says.

If that fails, I will look for some changes to Thunderbird's config files than force the use of insecure protocols. But really I would prefer not to show someone how to make their connection invisibly insecure.

You might contact cox and ask them if they consider their mail system HIPPA compliant. While it is not all that relevant in the consumer market, the guidelines regulate the use of encryption in the medical profession. Any doctor using Cox mail is failing in their compliance.

Oh and a link to the tests

Hi Matt,

I spent about an hour on the phone with Cox the other day (1st and 2nd level support). First level told me they aren't supposed to support e-mail clients, but tried to help anyway. He had me delete and create the IMAP account that I had already created just to see that I had done it correctly. What else to expect from first level. LOL

Second level looked at a few settings, but found nothing and finally admitted that Cox is having problems with e-mail clients, (Thunderbird, Apple mail, or others) where some people using the client have it work just fine and others have a problem. They know that it's happening, not WHY it's happening, nor WHAT to do about it. They are "working on it", with no ETA for a fix.

Cox Cable, hope you are monitoring these forums. This is a sorry state of affairs.

Matt, thanks for your research on the security issue. Think I'll give them a call back and jack them up a bit about that as well. Seems like the only way that anything gets fixed these days is when enough people complain about it.

If anyone else finds a fix, please let me know.

Ralph