Are you talking about a pop or imap mail account? Do you use: Authentication Method: 'OAuth2' or 'Normal Password' For both incoming and outgoing server settings? Gmail prefer you to use Imap and OAuth2.

If using Authentication Method: 'OAuth2', do you have cookies enabled? They must be enabled to allow OAuth2. In versions 78* or later:

• Select 'Menu app icon' > 'Options/Preferences'
• In 'Options/Preferences' left Pane select Privacy & Security
• Select checkbox 'Accept cookies from sites'

Do you have a program on your computer that is set to clean up certain files like session, cache, passwords, cookies etc ? That program could be CCleaner or similar or some Anti-Virus programs can also clean up/delete these files. If yes, then you need to make Thunderbird profile folder exempt from scanning.

Hi thanks for your response most appreciated, my Version is v78.6.0 imap is enabled and OAuth2 is also enabled Op system is win7 Sorry I didn’t understand “Menu app” I tried clicking the Thunderbird icon but there was no Options/ Pref, I have tried sending mail with AV and Firewall off but to no avail, first when I tried to send an email the first message was imap google.com has disconnected, I have had this before but I can not remember how we cured it? I now get “Failed error 80004005 could not send using outgoing server smtp verify settings are correct, which I think they are smtp.gmail.com(default) port 465 is normal and I have also tried port 587 I don’t use CC but I do use “PrevaZer” Haven't found a function to exempt an app I have also set gmail accounts settings “Farwarding and pop/imap” to pop disabled and imap enabled, regards Robert

Could you please do the following?

1. Open the menu > Help > Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.com, paste the info from your Troubleshooting Information page, use the Create New Paste button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the link to your troubleshooting information you just copied.

Application Basics

   Name: Thunderbird
   Version: 78.6.0
   Build ID: 20201211152611
   Dist ID:

   Update 
   User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0
   OS: Windows_NT 6.1

   Launcher Process: Enabled
   Multiprocess Windows: 0/0
             Disabled
   Remote Processes: 0
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.gmail.com:993, SSL, OAuth2
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

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

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

 Extensions

       Amazon.co.uk
       1.1
       true
       amazon@search.mozilla.org

       Bing
       1.0
       true
       bing@search.mozilla.org

       DuckDuckGo
       1.0
       true
       ddg@search.mozilla.org

       Google
       1.0
       true
       google@search.mozilla.org

       Wikipedia (en)
       1.0
       true
       wikipedia@search.mozilla.org

       I Ex
       3.3.2
       false
       {3ed8cc52-86fc-4613-9026-c1ef969da4c3}

 Security

   Type: Name

     Antivirus:
     Antispyware:
     Firewall:

 Graphics

     Features
     Compositing: Direct3D 11
     Asynchronous Pan/Zoom: none
     WebGL 1 Driver WSI Info: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000035b17)

EGL_VERSION: 1.4 (ANGLE 2.1.0.6c72b64f910d) EGL_EXTENSIONS: EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled EGL_ANDROID_blob_cache EGL_ANDROID_recordable EGL_ANGLE_image_d3d11_texture EGL_ANGLE_create_context_backwards_compatible EGL_EXTENSIONS(nullptr): EGL_EXT_client_extensions EGL_EXT_platform_base EGL_EXT_platform_device EGL_ANGLE_platform_angle EGL_ANGLE_platform_angle_d3d EGL_ANGLE_device_creation EGL_ANGLE_device_creation_d3d11 EGL_ANGLE_experimental_present_path EGL_KHR_client_get_all_proc_addresses EGL_KHR_debug EGL_ANGLE_explicit_context EGL_ANGLE_feature_control

     WebGL 1 Driver Renderer: Google Inc. -- ANGLE (NVIDIA GeForce GTS 450 Direct3D11 vs_5_0 ps_5_0)
     WebGL 1 Driver Version: OpenGL ES 2.0.0 (ANGLE 2.1.0.6c72b64f910d)
     WebGL 1 Driver Extensions: GL_ANGLE_client_arrays GL_ANGLE_depth_texture GL_ANGLE_explicit_context GL_ANGLE_explicit_context_gles1 GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_instanced_arrays GL_ANGLE_lossy_etc_decode GL_ANGLE_memory_size GL_ANGLE_multi_draw GL_ANGLE_multiview_multisample GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control GL_ANGLE_provoking_vertex GL_ANGLE_request_extension GL_ANGLE_robust_client_memory GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ANGLE_texture_usage GL_ANGLE_translated_shader_source GL_CHROMIUM_bind_generates_resource GL_CHROMIUM_bind_uniform_location GL_CHROMIUM_color_buffer_float_rgb GL_CHROMIUM_color_buffer_float_rgba GL_CHROMIUM_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_lose_context GL_CHROMIUM_sync_query GL_EXT_blend_func_extended GL_EXT_blend_minmax GL_EXT_color_buffer_half_float GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_float_blend GL_EXT_frag_depth GL_EXT_instanced_arrays GL_EXT_map_buffer_range GL_EXT_occlusion_query_boolean GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_shader_texture_lod GL_EXT_texture_compression_bptc GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc_srgb GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_unpack_subimage GL_KHR_debug GL_KHR_parallel_shader_compile GL_KHR_robust_buffer_access_behavior GL_NV_EGL_stream_consumer_external GL_NV_fence GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EGL_image_external GL_OES_depth24 GL_OES_depth32 GL_OES_element_index_uint GL_OES_get_program_binary GL_OES_mapbuffer GL_OES_packed_depth_stencil GL_OES_rgb8_rgba8 GL_OES_standard_derivatives GL_OES_surfaceless_context GL_OES_texture_3D GL_OES_texture_border_clamp GL_OES_texture_float GL_OES_texture_float_linear GL_OES_texture_half_float GL_OES_texture_half_float_linear GL_OES_texture_npot GL_OES_vertex_array_object OES_compressed_EAC_R11_signed_texture OES_compressed_EAC_R11_unsigned_texture OES_compressed_EAC_RG11_signed_texture OES_compressed_EAC_RG11_unsigned_texture OES_compressed_ETC2_RGB8_texture OES_compressed_ETC2_RGBA8_texture OES_compressed_ETC2_punchthroughA_RGBA8_texture OES_compressed_ETC2_punchthroughA_sRGB8_alpha_texture OES_compressed_ETC2_sRGB8_alpha8_texture OES_compressed_ETC2_sRGB8_texture
     WebGL 1 Extensions: ANGLE_instanced_arrays EXT_blend_minmax EXT_color_buffer_half_float EXT_float_blend EXT_frag_depth EXT_shader_texture_lod EXT_sRGB EXT_texture_compression_bptc EXT_texture_filter_anisotropic MOZ_debug OES_element_index_uint OES_standard_derivatives OES_texture_float OES_texture_float_linear OES_texture_half_float OES_texture_half_float_linear OES_vertex_array_object WEBGL_color_buffer_float WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_depth_texture WEBGL_draw_buffers WEBGL_lose_context
     WebGL 2 Driver WSI Info: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000035b17)

EGL_VERSION: 1.4 (ANGLE 2.1.0.6c72b64f910d) EGL_EXTENSIONS: EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled EGL_ANDROID_blob_cache EGL_ANDROID_recordable EGL_ANGLE_image_d3d11_texture EGL_ANGLE_create_context_backwards_compatible EGL_EXTENSIONS(nullptr): EGL_EXT_client_extensions EGL_EXT_platform_base EGL_EXT_platform_device EGL_ANGLE_platform_angle EGL_ANGLE_platform_angle_d3d EGL_ANGLE_device_creation EGL_ANGLE_device_creation_d3d11 EGL_ANGLE_experimental_present_path EGL_KHR_client_get_all_proc_addresses EGL_KHR_debug EGL_ANGLE_explicit_context EGL_ANGLE_feature_control

     WebGL 2 Driver Renderer: Google Inc. -- ANGLE (NVIDIA GeForce GTS 450 Direct3D11 vs_5_0 ps_5_0)
     WebGL 2 Driver Version: OpenGL ES 3.0.0 (ANGLE 2.1.0.6c72b64f910d)
     WebGL 2 Driver Extensions: GL_ANGLE_client_arrays GL_ANGLE_copy_texture_3d GL_ANGLE_depth_texture GL_ANGLE_explicit_context GL_ANGLE_explicit_context_gles1 GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_instanced_arrays GL_ANGLE_lossy_etc_decode GL_ANGLE_memory_size GL_ANGLE_multi_draw GL_ANGLE_multiview_multisample GL_ANGLE_pack_reverse_row_order GL_ANGLE_program_cache_control GL_ANGLE_provoking_vertex GL_ANGLE_request_extension GL_ANGLE_robust_client_memory GL_ANGLE_texture_compression_dxt3 GL_ANGLE_texture_compression_dxt5 GL_ANGLE_texture_multisample GL_ANGLE_texture_usage GL_ANGLE_translated_shader_source GL_CHROMIUM_bind_generates_resource GL_CHROMIUM_bind_uniform_location GL_CHROMIUM_color_buffer_float_rgb GL_CHROMIUM_color_buffer_float_rgba GL_CHROMIUM_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_lose_context GL_CHROMIUM_sync_query GL_EXT_blend_func_extended GL_EXT_blend_minmax GL_EXT_color_buffer_float GL_EXT_color_buffer_half_float GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_float_blend GL_EXT_frag_depth GL_EXT_instanced_arrays GL_EXT_map_buffer_range GL_EXT_occlusion_query_boolean GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_shader_texture_lod GL_EXT_texture_compression_bptc GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc_srgb GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_norm16 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_unpack_subimage GL_KHR_debug GL_KHR_parallel_shader_compile GL_KHR_robust_buffer_access_behavior GL_NV_EGL_stream_consumer_external GL_NV_fence GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EG

I hope the last post contains what you need, is there anything else I need to send, regards Robert

It contains what I expected, but not anything that will offer an answer. So I have been googling the error code looking for clues. Norton's anti virus product got a mention, but your posted information suggests NO anti virus others suggested windows corruption and yet others suggested extended windows characters. But given the wide options suggested I wonder if it might be something more simplistic and common. SO please go to the options on the menu and search cache. Then click the clear button.

Then go back to the troubleshooting information and in the "modified preferences" what is listed for

network.cookie.alwaysAcceptSessionCookies

I would expect true.

Hi Matt, thanks for your help, My Firewall is Comodo and the AV is Avast both have been told Thunderbird is safe

There is a cogwheel with options on the dashboard and I have tried that and also > Tools > Options, but I cannot see any Cache listed.

Now besides the " warning “server imap.gmail has disconnected” the Thunderbird will not send mail out, yet the parameters seem to be all ok, although I can still receive mail ok.

I would try to uninstall T'Bird and reinstall it, but last time I played with my email prog I lost a lot of folders with lots of saved stuff I needed

Windows NT 6.1

Extended support for Win7 ended on January 14, 2020. Time for an upgrade?

My Firewall is Comodo

Why exactly do you need a 3rd-party firewall for? Why aren't you just using the Windows built-in Firewall?

and the AV is Avast

Avast has a long history for causing problems with Thunderbird. See https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#AVAST

Try to start Windows in safe mode with networking enabled. Does the problem go away?

I would try to uninstall T'Bird and reinstall it

You'd be wasting your time.

re :but I do use “PrevaZer”

I suspect that cleanup app has removed a cookie or password or someother necessary info or corrupted a file etc. Probably a good idea to check settings, then remove passwords and reset the OAuth connection.

Server settings:

 INCOMING: account1, , (imap) imap.gmail.com:993, SSL, OAuth2
 OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

This looks correct, but you need to be sure the 'Username' in the outgoing smtp server has your full email address. So check it is correct.

Check cookies are ok:

• Select 'Menu app icon' > 'Options'
• In 'Options' left Pane select 'Privacy & Security'
• Select checkbox 'Accept cookies from sites'

In same area - 'Privacy & Security' - under 'Passwords' click on 'Saved Passwords' button Select the gmail account lines and click on 'Remove' click on Close

Exit Thunderbird.

Restart Thunderbird

Enter the gmail email address password in the OAuth browser window when prompted and allow Thunderbird access.

re: Sorry I didn’t understand “Menu app”

• The menu app icon The image "fx57menu" does not exist., has 3 horizontal lines.

Hi Guys, I appreciate your help, I think the problem is wrapped up with Google, and as I was trying your suggestions I Selected the gmail account lines and deleted them and also all my google PW's from my Dashline PW manager, when I tried to login to Chrome an old email address was auto entered, then an old PW, once I had entered the correct ones I checked again and the parameters were imap.gmail port 993 and smtp was port 587 I was able to send an email to myself using Thunderbird, but Chrome is using an old username, and when I hover on the little icon "top right" it shows the username which I tried to change, and "PAUSED" when I change this feature back to Sync it changes back to paused and "not signed in" on a Chrome reboot, so my having a gmail email address might be part of the problem.

As for Win7 I would like to keep it as long as I can because I like it, and many years ago all the tech experts said M'Soft FireWall and AV was very poor so I have used Avast & Comodo quite happily with Thunderbird for over ten years, & I haven't had a nasty on my PC for many years so I'm happy, has Win Firewall got better press now, what do you recommend? Thanks for your help, regards Robert

Hi again, today I tried to send a mail and it failed the message was "incorrect greeting" this afternoon it sent, but when I receive mail it still takes forever to download and I get the message that connection has broken, hours later the messages are in the inbox, there is a little elongated yellow box at the bottom of the screen with 82% in it and at the top I think is something to do with google because it says "Sync Paused" when I click on it and sign in it goes into sync (whatever sync does?) but if I close Chrome and then restart it is in paused mode again, do you think this has anything to do with google stopping Thunderbird from working, regards Robert

Sync is the "method" how TB communicate with gmail servers (or any imap server) Try starting TB in safe-mode (hold Shift button on your keyboard while starting TB) and see if like this you can send/receive mails.

Hi thanks for your explanation of sync, but sorry that didn't work, now I keep getting the enter your PW box so I enter my google pw and that allows me to send an email but only once as I have to log in each time I start TB and I still get the "connection to the server broken" message, as an example if I send an email and then go to the Sent folder and click on the sent mail I get the "connection to the server broken" message, or if I receive a mail with attachments when I click on the attachment I get the "lost connection" message

Lets me say this simply. Get rid of your password manager where Thunderbird is concerned. It has it's own and most of the mystery password problems appear to relate to third party products happily offering u0p out of date passwords.

Have you changed your authentication method to oAuth? If you have you need to have cookies enabled so the authentication can actually work and store the results. I changed to oauth for google 2 years ago and have never need asked for a password since as Google keeps renewing the oauth tokens when needed.

When you use oauth you will see a series of dialogs delivered as web pages from google, including one where you have to explicitly allow Thunderbird access to your email. Once that is done authentication is done basically until you change your password on google and even then it might take months.

Hi Matt, Yes I have set the authentication method toAuth2 I use the Chrome browser and have now set the cookies to "Accept all cookies" and turned on "Clear cookies when quitting Chrome" I have been into google mail settings and checked that imap was being used, it was, and all the parameters look ok, I am sure that you are correct to say that it might be something more simplistic. Tuesday I went into the TB settings and removed all the PW's although I can't remember seeing any request to explicitly allow Thunderbird access to my Thunderbird email, I do have a google PW and that is what I have now started entering when TB requests a PW and I have just had another look at the TB password box and there are now two PW's listed the 13-1-21 is showing my google pw and the 10-1-21 is a long formula of numbers, do I need to remove this? Sorry not sure what u0p is I have again just sent myself a mail (no attachments) and it sent and received in a second but if I go to the Sent folder and click on a recent sent mail with attachments I get the "Server imap.gmail.com has disconnected" do you think the bar on the taskbar (next to the (Today pane) with 82% in it has anything to do with the problem? Many thanks for your time and help, regards Robert

Update, where I'm at, Hi again, I am now able to send and receive emails but I cannot open all of them immediately as most times I get the server disconnected message, if I come back to the inbox later they will open, if I send a mail then go to the sent items and click open I get the server disconnected message. Earlier I was informed by svlad that Sync is the "method" how TB communicates with gmail servers (or any imap server) I am wondering if this has something to do with my problem as on closing the browser-sync goes into "Pause" mode and I have to manually turn it back on. The box on the taskbar (next to the (Today pane) was showing 84% and I zapped all the dross I could find and it dropped to 82% but now it's back to 84% I wonder if maybe many mails are still on the server taking up room and stopping more recent received mail from opening?

 Thanks for your time and help, regards Robert

• https://stackoverflow.com/a/63255601/3553808 : info on How to Access WebMail Type Email-WebSite From TB-WebBrowser-Tab , How to Configure TB to allow very specific OAuth2 based site-addresses in Cookie-Exception list, etc, etc. (please upvote my Q+A both, inside the linked page, if its useful/helpful).