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

Thanks for your reply, here's what I get. I can't quite post it all as it's over the character limit but I will post the rest separately;

 Application Basics

   Name: Thunderbird
   Version: 115.12.2
   Build ID: 20240621154414
   Distribution ID:

   Update Channel: esr
   User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:115.0) Gecko/20100101 Thunderbird/115.12.2
   OS: Windows_NT 10.0 19045
   OS Theme:

   Launcher Process: Enabled
   Multiprocess Windows: 0/0
   Fission Windows: 0/0
             Enabled by default
   Remote Processes: 3
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false
   Memory Size (RAM): 7.9 GB
   Disk Space Available: 35.9 GB

 Mail and News Accounts
   account2:
     INCOMING: account2, , (none) Local Folders, 0, passwordCleartext

   account3:
     INCOMING: account3, , (pop3) mail.talktalk.net:995, SSL, passwordCleartext
     OUTGOING: , smtp.talktalk.net:587, SSL, passwordCleartext, true

   account4:
     INCOMING: account4, , (pop3) pop-mail.outlook.com:995, SSL, OAuth2
     OUTGOING: , smtp.office365.com:587, alwaysSTARTTLS, OAuth2, true

   account5:
     INCOMING: account5, , (imap) mail.vikingfund.co.uk:143, 0, passwordCleartext
     OUTGOING: , mail.vikingfund.co.uk:587, 0, passwordEncrypted, true

   account6:
     INCOMING: account6, , (pop3) pop.gmail.com:995, SSL, OAuth2
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

 Libraries

     Library
     Status
     Expected minimum version
     Version in use
     Path

     RNP (OpenPGP)
     OK
     0.17.0
     0.17.0+PR2073.MZLA.115.12.2
     C:\Program Files\Mozilla Thunderbird\rnp.dll

 Calendar Settings

   Home

     Name
     Value

     Name:
     Type: storage
     Disabled:
     Username:
     URI:
     Refresh Interval:
     Read-only:
     Suppress Alarms:
     Cache Enabled:
     iMIP Identity: id3
     iMIP Disabled:
     iMIP Account:
     Organiser 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:

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

     Extension: 1
     Isolated Web Content: 1
     GPU: 1

 Add-ons

     Name
     Type
     Version
     Enabled
     ID

       British English Dictionary (Marco Pinto)
       dictionary
       3.3.3
       true
       marcoagpinto@mail.telepac.pt

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

       Bing
       extension
       1.0
       true
       bing@search.mozilla.org

       Chambers (UK)
       extension
       1.0
       true
       chambers-en-GB@search.mozilla.org

       DuckDuckGo
       extension
       1.0
       true
       ddg@search.mozilla.org

       Google
       extension
       1.0
       true
       google@search.mozilla.org

       ImportExportTools NG
       extension
       14.0.3
       true
       ImportExportToolsNG@cleidigh.kokkini.net

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

       ImportExportTools
       extension
       3.3.2
       false
       {3ed8cc52-86fc-4613-9026-c1ef969da4c3}

       Manually sort folders
       extension
       2.3.0
       false
       tbsortfolders@xulforum.org

 Security Software

   Type: Name

     Antivirus: Norton 360
     Antispyware:
     Firewall: Norton 360

 Graphics

     Features
     Compositing: WebRender
     Asynchronous Pan/Zoom: wheel input enabled; touch input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled; smooth pinch-zoom enabled
     WebGL 1 Driver WSI Info: EGL_VENDOR: Google Inc. (Intel)

EGL_VERSION: 1.5 (ANGLE 2.1.19736 git hash: fa03ab3adeaf) 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 IsWebglOutOfProcessEnabled: 1

     WebGL 1 Driver Renderer: Google Inc. (Intel) -- ANGLE (Intel, Intel(R) HD Graphics 620 Direct3D11 vs_5_0 ps_5_0, D3D11-26.20.100.7463)
     WebGL 1 Driver Version: OpenGL ES 2.0.0 (ANGLE 2.1.19736 git hash: fa03ab3adeaf)
     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_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_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_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_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_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_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_provoking_vertex

Final part of the troubleshooting info;

WebGL 2 Driver WSI Info: EGL_VENDOR: Google Inc. (Intel)

EGL_VERSION: 1.5 (ANGLE 2.1.19736 git hash: fa03ab3adeaf) 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_

The correct incoming server is outlook.office365.com on 995 (POP) or 993 (IMAP):

https://support.mozilla.org/en-US/questions/1417298#answer-1588949