Apologies for the way the asterisks render here, they were meant as a separator.

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.

Please also add the result of these troubleshooting steps to your post

• Does Thunderbird work in TB Safe mode (see Thunderbird Safe Mode)?
• Do you use anti-virus and firewall software? What is the version?
• What is the exact error message?

Please post back with this information and any other questions you might have.

From TB Troubleshooting Information -

 Application Basics

   Name: Thunderbird
   Version: 52.2.1
   User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20170622064432
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

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

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

   account3:
     INCOMING: account3, , (pop3) precision-copywriting.com:110, plain, passwordCleartext
     OUTGOING: , cp02.jvzoohost.com:465, SSL, passwordCleartext, true

   account5:
     INCOMING: account5, , (imap) imap.googlemail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.googlemail.com:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (pop3) mail.activelightphotography.com:995, SSL, passwordCleartext
     OUTGOING: , cp02.jvzoohost.com:465, SSL, passwordCleartext, true

   account7:
     INCOMING: account7, , (imap) mountain-and-desert.com:993, SSL, passwordCleartext
     OUTGOING: , cp02.jvzoohost.com:465, SSL, passwordCleartext, true

   account8:
     INCOMING: account8, , (imap) cp02.jvzoohost.com:993, SSL, passwordCleartext
     OUTGOING: , cp02.jvzoohost.com:465, SSL, passwordCleartext, true

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

 Crash Reports
   https://crash-stats.mozilla.com/report/index/bp-75a8f847-754b-47e3-9835-1d4502160929 (9/29/2016)
   https://crash-stats.mozilla.com/report/index/bp-999feefc-8bfc-4ac6-91f3-3e81e2140103 (1/3/2014)
   https://crash-stats.mozilla.com/report/index/bp-101fc1a6-41e6-4a69-baef-409322131009 (10/9/2013)

 Extensions
   Lightning, 5.4.2.1, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   Provider for Google Calendar, 3.3, true, {a62ef8ec-5fdc-40c2-873c-223b8a6925cc}
   Xpunge, 0.6, true, {786abda0-fd14-d247-bf69-38b2fc18491b}

 Important Modified Preferences

   Name: Value

     accessibility.lastLoadDate: 1499831784
     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
     dom.apps.reset-permissions: true
     extensions.lastAppVersion: 52.2.1
     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: Verdana
     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: 15
     gfx.direct3d.last_used_feature_level_idx: 0
     mail.openMessageBehavior.version: 1
     mail.winsearch.enable: true
     mail.winsearch.firstRunDone: true
     mail.winsearch.global_reindex_time: 1381173819
     mailnews.database.global.datastore.id: a825c993-40c6-4ae1-bb81-cf864aaeacb
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"3"},"attachmentCol":{"visible":false…
     media.gmp.storage.version.observed: 1
     network.cookie.cookieBehavior: 3
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1499383476
     places.history.expiration.transient_current_max_pages: 122334
     plugin.importedState: true
     print.printer_Canon_MX520_series_Printer.print_bgcolor: false
     print.printer_Canon_MX520_series_Printer.print_bgimages: false
     print.printer_Canon_MX520_series_Printer.print_colorspace:
     print.printer_Canon_MX520_series_Printer.print_command:
     print.printer_Canon_MX520_series_Printer.print_downloadfonts: false
     print.printer_Canon_MX520_series_Printer.print_duplex: 8
     print.printer_Canon_MX520_series_Printer.print_edge_bottom: 0
     print.printer_Canon_MX520_series_Printer.print_edge_left: 0
     print.printer_Canon_MX520_series_Printer.print_edge_right: 0
     print.printer_Canon_MX520_series_Printer.print_edge_top: 0
     print.printer_Canon_MX520_series_Printer.print_evenpages: true
     print.printer_Canon_MX520_series_Printer.print_footercenter:
     print.printer_Canon_MX520_series_Printer.print_footerleft: &PT
     print.printer_Canon_MX520_series_Printer.print_footerright: &D
     print.printer_Canon_MX520_series_Printer.print_headercenter:
     print.printer_Canon_MX520_series_Printer.print_headerleft: &T
     print.printer_Canon_MX520_series_Printer.print_headerright: &U
     print.printer_Canon_MX520_series_Printer.print_in_color: true
     print.printer_Canon_MX520_series_Printer.print_margin_bottom: 0.5
     print.printer_Canon_MX520_series_Printer.print_margin_left: 0.5
     print.printer_Canon_MX520_series_Printer.print_margin_right: 0.5
     print.printer_Canon_MX520_series_Printer.print_margin_top: 0.5
     print.printer_Canon_MX520_series_Printer.print_oddpages: true
     print.printer_Canon_MX520_series_Printer.print_orientation: 0
     print.printer_Canon_MX520_series_Printer.print_page_delay: 50
     print.printer_Canon_MX520_series_Printer.print_paper_data: 1
     print.printer_Canon_MX520_series_Printer.print_paper_height: 11.00
     print.printer_Canon_MX520_series_Printer.print_paper_name:
     print.printer_Canon_MX520_series_Printer.print_paper_size_type: 0
     print.printer_Canon_MX520_series_Printer.print_paper_size_unit: 0
     print.printer_Canon_MX520_series_Printer.print_paper_width: 8.50
     print.printer_Canon_MX520_series_Printer.print_plex_name:
     print.printer_Canon_MX520_series_Printer.print_resolution: 0
     print.printer_Canon_MX520_series_Printer.print_resolution_name:
     print.printer_Canon_MX520_series_Printer.print_reversed: false
     print.printer_Canon_MX520_series_Printer.print_scaling: 1.00
     print.printer_Canon_MX520_series_Printer.print_shrink_to_fit: true
     print.printer_Canon_MX520_series_Printer.print_to_file: false
     print.printer_Canon_MX520_series_Printer.print_unwriteable_margin_bottom: 0
     print.printer_Canon_MX520_series_Printer.print_unwriteable_margin_left: 0
     print.printer_Canon_MX520_series_Printer.print_unwriteable_margin_right: 0
     print.printer_Canon_MX520_series_Printer.print_unwriteable_margin_top: 0
     privacy.sanitize.timeSpan: 0
     security.sandbox.content.tempDirSuffix: {562eed00-78dc-437f-a751-8060effd8704}

 Graphics

     GPU #1
     Description: NVIDIA GeForce GTX 750 Ti
     Vendor ID: 0x10de
     Device ID: 0x1380
     RAM: 4096
     Drivers: C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvd3dumx,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2umx,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2umx,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2umx C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvd3dum,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2um,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2um,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_f37f8f12da8b10d7\nvwgf2um
     Driver Version: 21.21.13.7892
     Driver Date: 3-16-2017

     Features
     Direct2D: false
     DirectWrite: true (10.0.15063.413)
     WebGL Renderer: Google Inc. -- ANGLE (NVIDIA GeForce GTX 750 Ti 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
     3.28.5
     3.28.5

     NSS Util
     3.28.5
     3.28.5

     NSS SSL
     3.28.5
     3.28.5

     NSS S/MIME
     3.28.5
     3.28.5

I get the same error in TB safe mode. Anti-virus software is AVG Internet Security, version 17.5.3021 (Last update on July 10, 2-17), with Virus definitions version 170710-18.

The exact error message is the same as in my initial post -

Error with account [email protected] Sending of password for user [email protected] did not succeed. Mail server inbound.att.net responded: Server error - Please try again later.

Based on the information here it looks to me like you need to change your server names to the new server supported by ATT.

POP3 inbound.att.net / 995 IMAP imap.mail.att.net / 993 with SSL SMTP smtp.mail.att.net / 465 or 587 with SSL

Username [email protected]

Please look at Mail and News Account account1 in the TB troubleshooting information. I should have stated that's AT&T.

The incoming and outgoing server names and ports are the same as you and AT&T suggest.

Unless I've missed something here.

You sure have missed something here.

From your troubleshooting information Mail and News Accounts

  account1:
    INCOMING: account1, , (pop3) inbound.att.net:995, SSL, passwordCleartext
    OUTGOING: , smtp.att.yahoo.com:465, SSL, passwordCleartext, true

What part of smtp.att.yahoo.com looks like smtp.mail.att.net Your outgoing setting are not correct. Despite what you have just said.

That said they are sending server settings and you say you can not receive. I find that odd, as if you have th right setting and credentials then all that is left is poor SSL

I checked their server here and it looks like they are still running with old SSL. So their mail servers may not be compatible with recent Thunderbird releases. The Diffie-Hellman parameter's size is only 1024 bits

Open the error console. (ctrl+Shift+J clear the existing stuff and try to get you mail. What errors appear. I have a feeling that 1024 should be 2048.

As a side note. ATT email with a 1024 is not legally usable for health related matters. Doctors and other health professionals would actually be breaking the law to use it. It is also not suitable for anyone processing credit card payments as it done not meet the card processors guidelines.

Matt - Sorry, saw smtp.mail.att.net listed in my outgoing servers, and discovered the att.net acct is using smtp.att.yahoo.com under its own settings. Sending email from that account works with smtp.att.yahoo.com, but doesn't with smtp.mail.att.net.

I've added a screen shot of the initial error console.

After clearing and trying to get mail, the error console looks like the second attached file (thunderbird after clr - a jpg file).

Still mysterious to me - uncaught exception errors. I was an analog IC design engineer, not a software / Windows / Unix guy.

Matt - Just changed my ATT password on their webmail once to a new one, then back to the original one. The POP settings still don't work, but I got IMAP to work now.

log into the Yahoo web mail. That is yahoo, not ATT using you ATT credentials. I did this once in the reverse, signed into Yahoo from ATT so I guess it will work.

Then follow the procedure Yahoo lay out to enable less secure apps.

I am guessing here, but I think that I am on the right path.

Enable less-secure apps is no longer an option in Yahoo's account security. All they let you do is change password, and that nos forwards to AT&T.

Logging into the att.net account doesn't give me that option either.

I'm happy with using the IMAP servers and settings in TB. It's probably more secure than POP3 anyway.

Thanks for your efforts.