I keep getting error messages.

What error exactly?

Like this:

What happens when you click on the 'add an exception' link? Note, you're not supposed to actually create an exception. The idea is to just get to a point where you can inspect the cert.

Also, what is your anti-virus/security software?

When I click "create an exception", nothing happens. At all. Screenshot of my Windows Security:

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.

(Had to clip some b/c of length)

 Application Basics

   Name: Thunderbird
   Version: 78.12.0
   Build ID: 20210712120515
   Distribution ID:

   Update Channel: release
   User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0
   OS: Windows_NT 10.0

   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

     Name
     Version
     Enabled
     ID

       Amazon.com
       1.1
       true
       amazondotcom@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

 Security Software

   Type: Name

     Antivirus: Microsoft Defender Antivirus
     Antispyware:
     Firewall:

 Graphics

     Features
     Compositing: Direct3D 11 (Advanced Layers)
     Asynchronous Pan/Zoom: none
     WebGL 1 Driver WSI Info: EGL_VENDOR: Google Inc. (adapter LUID: 000000000000f392)

EGL_VERSION: 1.5 (ANGLE 2.1.14226 git hash: 31a43497be09) 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_ANGLE_direct_composition 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_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_display_semaphore_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_KHR_create_context_no_error EGL_KHR_reusable_sync 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_platform_angle_d3d11on12 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 (Intel(R) UHD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
     WebGL 1 Driver Version: OpenGL ES 2.0.0 (ANGLE 2.1.14226 git hash: 31a43497be09)
     WebGL 1 Driver Extensions: GL_ANGLE_base_vertex_base_instance 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_get_tex_level_parameter 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_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_EGL_image_external_wrap_modes 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_draw_elements_base_vertex GL_EXT_float_blend GL_EXT_frag_depth GL_EXT_instanced_arrays GL_EXT_map_buffer_range GL_EXT_multisampled_render_to_texture 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_rgtc 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_no_error 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_compressed_EAC_R11_signed_texture GL_OES_compressed_EAC_R11_unsigned_texture GL_OES_compressed_EAC_RG11_signed_texture GL_OES_compressed_EAC_RG11_unsigned_texture GL_OES_compressed_ETC2_RGB8_texture GL_OES_compressed_ETC2_RGBA8_texture GL_OES_compressed_ETC2_punchthroughA_RGBA8_texture GL_OES_compressed_ETC2_punchthroughA_sRGB8_alpha_texture GL_OES_compressed_ETC2_sRGB8_alpha8_texture GL_OES_compressed_ETC2_sRGB8_texture GL_OES_depth24 GL_OES_depth32 GL_OES_draw_elements_base_vertex GL_OES_element_index_uint GL_OES_fbo_render_mipmap 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_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_texture_stencil8 GL_OES_vertex_array_object GL_WEBGL_video_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_compression_rgtc EXT_texture_filter_anisotropic MOZ_debug OES_element_index_uint OES_fbo_render_mipmap 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: 000000000000f392)

EGL_VERSION: 1.5 (ANGLE 2.1.14226 git hash: 31a43497be09) 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_ANGLE_direct_composition 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_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_display_semaphore_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_KHR_create_context_no_error EGL_KHR_reusable_sync 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_platform_angle_d3d11on12 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 (Intel(R) UHD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
     WebGL 2 Driver Version: OpenGL ES 3.0.0 (ANGLE 2.1.14226 git hash: 31a43497be09)
     WebGL 2 Driver Extensions: GL_ANGLE_base_vertex_base_instance GL_ANGLE_client_arrays

Your email account settings look good, and it's highly unlikely that anti-virus is interfering with your secure connection to the server. Are you certain this error is related to email? What happens if you close the error? Can you still get mail? Is it possible the error is generated by a Google Calendar?

I've restarted TBird and the PC itself numerous times since yesterday - always the same. I don't use Google Calendar. Any other way Google may have caused this? It just came out of the blue yesterday morning.

Do you have a VPN? If so, is there still a problem if you turn it off?

No VPN. In fact I had to Google it to find out what it is! :)

Do you accept cookies in TB Options/Privacy & Security? That's necessary for OAuth authentication to complete, although a different error message is usually presented. As a test, try adding the account to a new profile from Help/Troubleshooting, about:profiles. The original profile is not affected.

I tried this, and this time I got a different error. It doesn't seem to "know" that telus.net is now using gmail. Would this make a difference?

The correct settings for Telus are: imap.gmail.com on 993, SSL/TLS, OAuth2, smtp.gmail.com on 465, SSL/TLS, or 587, STARTTLS; OAuth2. User Name for both is yourname@telus.net. You might have to use Manual config. when adding the account, as the TB database is obviously out of date (Telus has used gmail for several months).

the TB database is obviously out of date (Telus has used gmail for several months).

Has a bug been filed to update the database do you know?

OK, I tried that, and here's the latest error message. Did I mess it up by creating a new password for this profile?

Bit of an experiment here but try going here https://myaccount.google.com/lesssecureapps and turning on less secure apps. While it should be kicking off an oAuth sign in attempt, it might be still trying with a normal password and that setting will allow it to succeed.

If that does work I would ask you to document the exact steps I would need to replicate your failure.

OK, I tried that, and here's the latest error message. Did I mess it up by creating a new password for this profile?

Did you confirm the new password by logging in on the gmail website?

If you use OAuth2 with the correct password, the 'less-secure apps' and two-factor verification settings are irrelevant.

The new password did NOT work when I tried to log into gmail. The original password did work. But when I did your new profile exercise again, with the original password, I still got the error message.

Fixed. Here's what happened. I had my webmistress go into my computer remotely. She clicked on the "Create an Exception" button and, like me, had no visible result. She then closed the error window (which I hadn't done when I selected that option before) and suddenly the Authentication worked! Hopefully one of the TB techs can fix this bug so that the re-authentication process can work without having to accidentally stumble on it. :)

I did the same thing which makes the Secure Connection Failed pop-up message go away but after a while it comes back and I have to close the pop-up again. This error message only started appearing when I installed TB on my new Windows 11 laptop. My other PC's run Windows 10 and do not get the error message.