Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

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, , (pop3) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.aol.com:465, SSL, passwordCleartext, true

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

 Crash Reports

 Extensions
   ImportExportTools, 3.3.0, true, {3ed8cc52-86fc-4613-9026-c1ef969da4c3}
   Lightning, 5.4.6, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}

 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
     browser.zoom.full: true
     dom.apps.reset-permissions: true
     dom.max_chrome_script_run_time: 0
     extensions.lastAppVersion: 52.6.0
     font.internaluseonly.changed: true
     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: 12
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 6d1ea490-f7da-4f96-b396-54511ce6951
     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.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1519910946
     places.history.expiration.transient_current_max_pages: 64443
     plugin.importedState: true
     print.printer_HP_Photosmart_Wireless_B109n-z.print_bgcolor: false
     print.printer_HP_Photosmart_Wireless_B109n-z.print_bgimages: false
     print.printer_HP_Photosmart_Wireless_B109n-z.print_duplex: -437918235
     print.printer_HP_Photosmart_Wireless_B109n-z.print_edge_bottom: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_edge_left: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_edge_right: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_edge_top: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_evenpages: true
     print.printer_HP_Photosmart_Wireless_B109n-z.print_footercenter:
     print.printer_HP_Photosmart_Wireless_B109n-z.print_footerleft: &PT
     print.printer_HP_Photosmart_Wireless_B109n-z.print_footerright: &D
     print.printer_HP_Photosmart_Wireless_B109n-z.print_headercenter:
     print.printer_HP_Photosmart_Wireless_B109n-z.print_headerleft: &T
     print.printer_HP_Photosmart_Wireless_B109n-z.print_headerright: &U
     print.printer_HP_Photosmart_Wireless_B109n-z.print_in_color: true
     print.printer_HP_Photosmart_Wireless_B109n-z.print_margin_bottom: 0.5
     print.printer_HP_Photosmart_Wireless_B109n-z.print_margin_left: 0.5
     print.printer_HP_Photosmart_Wireless_B109n-z.print_margin_right: 0.5
     print.printer_HP_Photosmart_Wireless_B109n-z.print_margin_top: 0.5
     print.printer_HP_Photosmart_Wireless_B109n-z.print_oddpages: true
     print.printer_HP_Photosmart_Wireless_B109n-z.print_orientation: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_page_delay: 50
     print.printer_HP_Photosmart_Wireless_B109n-z.print_paper_data: 9
     print.printer_HP_Photosmart_Wireless_B109n-z.print_paper_height: -1.00
     print.printer_HP_Photosmart_Wireless_B109n-z.print_paper_name:
     print.printer_HP_Photosmart_Wireless_B109n-z.print_paper_size_unit: 1
     print.printer_HP_Photosmart_Wireless_B109n-z.print_paper_width: -1.00
     print.printer_HP_Photosmart_Wireless_B109n-z.print_resolution: 600
     print.printer_HP_Photosmart_Wireless_B109n-z.print_reversed: false
     print.printer_HP_Photosmart_Wireless_B109n-z.print_scaling: 0.80
     print.printer_HP_Photosmart_Wireless_B109n-z.print_shrink_to_fit: true
     print.printer_HP_Photosmart_Wireless_B109n-z.print_to_file: false
     print.printer_HP_Photosmart_Wireless_B109n-z.print_unwriteable_margin_bottom: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_unwriteable_margin_left: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_unwriteable_margin_right: 0
     print.printer_HP_Photosmart_Wireless_B109n-z.print_unwriteable_margin_top: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_bgcolor: false
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_bgimages: false
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_duplex: -437918235
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_edge_bottom: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_edge_left: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_edge_right: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_edge_top: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_evenpages: true
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_footercenter:
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_footerleft: &PT
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_footerright: &D
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_headercenter:
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_headerleft: &T
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_headerright: &U
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_in_color: true
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_margin_bottom: 0.5
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_margin_left: 0.5
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_margin_right: 0.5
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_margin_top: 0.5
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_oddpages: true
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_orientation: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_page_delay: 50
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_data: 9
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_height: 11.00
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_name:
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_size_type: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_size_unit: 1
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_paper_width: 8.50
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_resolution: -437918235
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_reversed: false
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_scaling: 1.00
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_shrink_to_fit: true
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_to_file: false
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_unwriteable_margin_bottom: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_unwriteable_margin_left: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_unwriteable_margin_right: 0
     print.printer_HPEFC3CD_(HP_Photosmart_Wireless_B109n-z).print_unwriteable_margin_top: 0
     privacy.donottrackheader.enabled: true
     security.sandbox.content.tempDirSuffix: {062ea326-9a4c-4a2c-a192-4ad3642f3ad1}

 Graphics

     GPU #1
     Description: Intel(R) HD Graphics
     Vendor ID: 0x8086
     Device ID: 0x1606
     RAM: Unknown
     Drivers: igdumdim64 igd10iumd64 igd10iumd64 igd12umd64 igdumdim32 igd10iumd32 igd10iumd32 igd12umd32
     Driver Version: 20.19.15.4549
     Driver Date: 11-10-2016

     Features
     Direct2D: false
     DirectWrite: true (10.0.16299.15)
     ClearType Parameters: Gamma: 2.2 Pixel Structure: RGB ClearType Level: 100 Enhanced Contrast: 300
     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)

Thank you. I was told I had 40 characters too many, so here is the rest of it:-

    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

Instead of SMTP 465, I just tried 587, but the same appeared:- An error occurred with the POP3 mail server. Mail server imap.aol.com responded:

Yesterday, I read somewhere to try disabling the antivirus mail shield so I did that but matters stayed the same.

I am very lucky that, some while ago, I downloaded windows live mail so at least I can send and receive emails through that for now.

INCOMING: account1, , (pop3) imap.aol.com:993, SSL, passwordCleartext

You've set up your account as POP, but gave it an IMAP server. Set the correct server for POP.

Instead of SMTP 465, I just tried 587 but the same appeared:- An error occurred with the POP3 mail server.

You've been messing with the outgoing server, but your problem is with the incoming server.

OUTGOING: , smtp.aol.com:465, SSL, passwordCleartext, true

SMTP server settings look good. What prevents you from sending messages?

I had been receiving and sending emails without problems but suddenly I could not receive them and later in the day couldn't send any as well. That happened without having made any changes.

When I received an email from AOL in October last year saying I had to update connection settings, I visited their help site for instructions on how to update the settings and did whatever it said. I made no changes since then until this problem occurred.

How do I give it a correct server for POP, please? I tried going to account settings and in server settings changed the server name to pop.aol.com. When I clicked on get messages, this appeared:- Failed to connect to server pop.aol.com.

I don't know what is preventing me from sending messages. I just tried sending one to myself and the following appeared immediately: Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) smtp.aol.com timed out. Try again.

PS I changed pop.aol.com to 995 and emails came in. Excellent! :-)

However, the outgoing is still the same as above:- The message could not be sent because the connection to Outgoing server (SMTP) smtp.aol.com timed out. Try again.

How do I give it a correct server for POP, please?

You had the correct information already: https://help.aol.co.uk/articles/how-do-i-use-other-email-applications-to-send-and-receive-my-aol-mail

Look up the correct server for POP in the support article, and then adjust the server setting in Thunderbird accordingly.

The message could not be sent because the connection to Outgoing server (SMTP) smtp.aol.com timed out. Try again.

If you're running any kind of 'security' software make sure it isn't blocking Thunderbird outgoing connections.

I had to enter my password for incoming emails. I just tried changing, again, the number for outgoing to 465, and had to enter my password. Both worked! I wonder why it worked before and then didn't.

When your problem is fixed, can you mark the topic as 'Solved' please? Thank you.

Thank you. Strangely previously (that I had printed some while ago), in https://help.aol.co.uk/articles/how-do-i-use-other-email-applications-to-send-and-receive-my-aol-mail was "Your email client might prompt you to select either IMAP or POP3. AOL Mail supports both, but we recommend using IMAP.".

I had to enter the password again just now and clicked on password manager to remember it. Fingers crossed! And thank you again for your help and patience.