If you could supply the error messages that accompany these issues perhaps someone could guess, but the description you have so far could just as easily describe a visually impaired person walking into a fence. Something keeps stopping them walking forward, they have no idea what it is, but they know they can not go there.

(That person was my brother-in-law by the way. I am not making it up.)

I can say that certain antivirus products make a habit of preventing mail connections, so do some VPN's with some providers (many mail providers will guess you have been hacked if you use a VPN and raise a flag/alert instead of letting you in.) Others lock account for sending spam, or to many wrong passwords (that was a bug in the not so distant past where Thunderbird would retry a failed connection and the provider would disable the account)

But really I am just offering some suggestions off the top of my head because I have no specifics to work with, but by far the most likely cause of a failure to get mail after an upgrade/update will be your antivirus/ Software firewall.

Hi Matt,

Thanks for your thoughtful response. The error I get says, Login Failed. There's additional stuff about not being able to log into the server. I'll have to wait for the problem to recur to get you the complete message unless there's a log file hiding somewhere. Do you know?

By the way, it's working fine today and I changed nothing.

Will post an update next time it happens.

This is an ongoing problem. Yesterday, everything worked fine. Today, none of my accounts (two Yahoo, one Gmail) is able to log into their respective servers. Here's the error:

What is your anti-virus software?

Also, 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.

I am using AVG antivirus.

Here's the troubleshooting information:

 Application Basics

   Name: Thunderbird
   Version: 139.0.2
   Build ID: 20250606205843
   Distribution ID:

   Update Channel: release
   User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:139.0) Gecko/20100101 Thunderbird/139.0.2
   OS: Windows_NT 10.0 19045
   OS Theme:

   Launcher Process: Enabled
   Multiprocess Windows: 0/0
   Fission Windows: 0/0
             Enabled by default
   Remote Processes: 1
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false
   Memory Size (RAM): 31.9 GB
   Disk Space Available: 119 GB

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.mail.yahoo.com:993, 3, 10
     OUTGOING: , smtp.mail.yahoo.com:465, 3, 10, true

   account2:
     INCOMING: account2, , (none) Local Folders, 0, 3

   account3:
     INCOMING: account3, , (imap) imap.mail.yahoo.com:993, 3, 10
     OUTGOING: , smtp.mail.yahoo.com:465, 3, 10, true

   account4:
     INCOMING: account4, , (imap) imap.gmail.com:993, 3, 10
     OUTGOING: , smtp.gmail.com:465, 3, 10, true

 Libraries

     Library
     Status
     Expected minimum version
     Version in use
     Path

       RNP (OpenPGP)
       OK
       0.17.1
       0.17.1.MZLA.139.0.2.botan
       C:\Program Files\Mozilla Thunderbird\rnp.dll

       OTR
       Failed to load. OTR chat encryption will not work.
       -
       -
       -

 Calendar Settings

     Home

       Name
       Value

       Name:
       Type: storage
       Disabled: false
       Username:
       URI:
       Refresh Interval:
       Read-only:
       Suppress Alarms:
       Cache Enabled:
       iMIP Identity: id1
       iMIP Disabled:
       iMIP Account:
       Organizer Id:
       Force Email Scheduling:
       Popup Alarms Supported:
       Alarms on Invitation Supported:
       Max Alarms Per Event:
       Attachment Supported:
       Max Categories:
       Privacy State Supported:
       Priority Supported: true
       Event Supported:
       Task Supported:
       Local Time Supported:
       UTC/GMT Supported:
       Auto-Scheduling Supported:

     invite(1)

       Name
       Value

       Name:
       Type: ics
       Disabled:
       Username:
       URI:
       Refresh Interval:
       Read-only:
       Suppress Alarms:
       Cache Enabled:
       iMIP Identity: id1
       iMIP Disabled:
       iMIP Account:
       Organizer Id:
       Force Email Scheduling:
       Popup Alarms Supported:
       Alarms on Invitation Supported:
       Max Alarms Per Event:
       Attachment Supported:
       Max Categories:
       Privacy State Supported:
       Priority Supported:
       Event Supported:
       Task Supported:
       Local Time Supported:
       UTC/GMT Supported:
       Auto-Scheduling Supported:

     invite

       Name
       Value

       Name:
       Type: ics
       Disabled:
       Username:
       URI:
       Refresh Interval:
       Read-only:
       Suppress Alarms:
       Cache Enabled:
       iMIP Identity: id1
       iMIP Disabled:
       iMIP Account:
       Organizer Id:
       Force Email Scheduling:
       Popup Alarms Supported:
       Alarms on Invitation Supported:
       Max Alarms Per Event:
       Attachment Supported:
       Max Categories:
       Privacy State Supported:
       Priority Supported:
       Event Supported:
       Task Supported:
       Local Time Supported:
       UTC/GMT Supported:
       Auto-Scheduling Supported:

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

   GPU: 1

 Add-ons

     Name
     Type
     Version
     Enabled
     Location
     ID

       System theme — auto
       theme
       1.4.1
       true
       app-builtin
       default-theme@mozilla.org

       Dark
       theme
       1.3
       false
       app-builtin
       thunderbird-compact-dark@mozilla.org

       Light
       theme
       1.3
       false
       app-builtin
       thunderbird-compact-light@mozilla.org

 Security Software

   Type: Name

     Antivirus:
     Antispyware:
     Firewall:

 Legacy User Stylesheets

   Active: false
   Stylesheets: No stylesheets found

 Graphics

     Features
     Compositing: WebRender
     Font Visibility Debug Info: Windows Platform
     Asynchronous Pan/Zoom: wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled; smooth pinch-zoom enabled
     WebGL 1 Driver WSI Info: outOfProcess: false

inProcess: true EGL_VENDOR: Google Inc. (AMD) EGL_VERSION: 1.5 (ANGLE 2.1.19739 git hash: 419cd2c3213b) 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_ANGLE_windows_ui_composition EGL_NV_post_sub_buffer EGL_KHR_create_context 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_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_no_config_context EGL_KHR_create_context_no_error EGL_KHR_reusable_sync EGL_EXTENSIONS(nullptr): EGL_EXT_client_extensions EGL_EXT_device_query EGL_EXT_platform_base EGL_EXT_platform_device EGL_ANGLE_platform_angle EGL_ANGLE_platform_angle_d3d EGL_ANGLE_platform_angle_d3d11on12 EGL_ANGLE_platform_angle_device_id 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_feature_control

     WebGL 1 Driver Renderer: Google Inc. (AMD) -- ANGLE (AMD, Radeon (TM) Pro WX 7100 Graphics Direct3D11 vs_5_0 ps_5_0, D3D11-30.0.13018.2)
     WebGL 1 Driver Version: OpenGL ES 3.0.0 (ANGLE 2.1.19739 git hash: 419cd2c3213b)
     WebGL 1 Driver Extensions: GL_AMD_performance_monitor GL_ANGLE_base_vertex_base_instance GL_ANGLE_base_vertex_base_instance_shader_builtin GL_ANGLE_client_arrays GL_ANGLE_copy_texture_3d GL_ANGLE_depth_texture GL_ANGLE_framebuffer_blit GL_ANGLE_framebuffer_multisample GL_ANGLE_get_serialized_context_string 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_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_copy_compressed_texture GL_CHROMIUM_copy_texture GL_CHROMIUM_lose_context GL_CHROMIUM_sync_query GL_EXT_EGL_image_external_wrap_modes GL_EXT_base_instance GL_EXT_blend_func_extended GL_EXT_blend_minmax GL_EXT_clip_control GL_EXT_color_buffer_float GL_EXT_color_buffer_half_float GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_disjoint_timer_query GL_EXT_draw_buffers GL_EXT_draw_buffers_indexed 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_multi_draw_indirect 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_norm16 GL_EXT_texture_rg GL_EXT_texture_storage GL_EXT_texture_type_2_10_10_10_REV 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_framebuffer_blit GL_NV_pack_subimage GL_NV_pixel_buffer_object GL_OES_EGL_image GL_OES_EGL_image_external GL_OES_EGL_image_external_essl3 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_buffers_indexed 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

I am using AVG antivirus.

Try to start Windows 10 in safe mode with networking enabled.

Still in Windows safe mode, start Thunderbird in troubleshooting mode. Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.