In order for us to better investigate this issue you need to add a little more non-personal information.

Please add the troubleshooting information to your post To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

sagan.gangadharan said

There are no changes in the mail server settings. Post upgrading to thunderbird 38.1.0 I am getting the following error while sending mails. Sending of the message failed. The message could not be sent using Outgoing server (SMTP) mail.hclinsys.com for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again.

The problem is with acccount 1only.

 Application Basics

   Name: Thunderbird
   Version: 38.1.0
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20150707103124
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (pop3) mail.hclinsys.com:995, SSL, 0
     OUTGOING: mail.hclinsys.com:2525, alwaysSTARTTLS, passwordCleartext, true

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

   account5:
     INCOMING: account5, , (pop3) mail.hclinsys.com:995, SSL, passwordCleartext
     OUTGOING: mail.hclinsys.com:2525, plain, passwordCleartext, true
     OUTGOING: mail.hclinsys.com:2525, alwaysSTARTTLS, passwordCleartext, false

   account18:
     INCOMING: account18, , (im) prpl-gtalk, plain, 0

   account19:
     INCOMING: account19, , (pop3) pop.uidai.net.in:995, SSL, passwordCleartext
     OUTGOING: smtp.uidai.net.in:465, SSL, passwordCleartext, true

   account20:
     INCOMING: account20, , (pop3) imap.uidai.net.in:995, SSL, passwordCleartext
     OUTGOING: smtp.uidai.net.in:465, SSL, passwordCleartext, true

 Crash Reports
   http://crash-stats.mozilla.com/report/index/bp-283d8f6c-d8d0-4e2e-ac2a-70a712141126 (26-11-2014)
   http://crash-stats.mozilla.com/report/index/bp-3594daac-5e7b-4ae5-a572-af61d2140827 (27-08-2014)
   http://crash-stats.mozilla.com/report/index/bp-8003265a-65ed-450e-9e28-d78262140113 (13-01-2014)
   http://crash-stats.mozilla.com/report/index/bp-9c684805-a05e-45b4-bcf9-f25c12130702 (02-07-2013)
   http://crash-stats.mozilla.com/report/index/bp-77abe6d7-ef4f-488c-a703-db1742130701 (01-07-2013)

 Extensions
   CALDAV - Search/Subscribe, 0.2, true, caldav-search@nomail
   Duplicate Contact Manager, 0.9.2, true, {b4447f60-db9c-11da-a94d-0800200c9a66}
   Google Tasks Sync, 0.5.2, true, [email protected]
   Lightning, 4.0.1, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   LookOut, 1.2.13, true, [email protected]
   Maximize Message Pane, 1.1.16, true, {CC1FC7EB-79F7-4A28-B12C-731304F16E53}
   Provider for Google Calendar, 1.0.4, true, {a62ef8ec-5fdc-40c2-873c-223b8a6925cc}
   Remove Duplicate Messages, 0.1.14, true, {12345678-1234-1234-1234-123456789abc}

 Important Modified Preferences

   Name: Value

     accessibility.typeaheadfind.flashBar: 0
     browser.cache.disk.capacity: 358400
     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
     dom.max_chrome_script_run_time: 0
     extensions.lastAppVersion: 38.1.0
     font.internaluseonly.changed: false
     font.name.monospace.el: Consolas
     font.name.monospace.tr: Consolas
     font.name.monospace.x-baltic: Consolas
     font.name.monospace.x-central-euro: 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.tr: Calibri
     font.name.sans-serif.x-baltic: Calibri
     font.name.sans-serif.x-central-euro: 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.tr: Cambria
     font.name.serif.x-baltic: Cambria
     font.name.serif.x-central-euro: 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.tr: 14
     font.size.fixed.x-baltic: 14
     font.size.fixed.x-central-euro: 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.tr: 17
     font.size.variable.x-baltic: 17
     font.size.variable.x-central-euro: 17
     font.size.variable.x-cyrillic: 17
     font.size.variable.x-unicode: 17
     font.size.variable.x-western: 17
     gfx.direct3d.last_used_feature_level_idx: 0
     mail.openMessageBehavior.version: 1
     mail.winsearch.firstRunDone: true
     mailnews.database.global.datastore.id: 843b8cb6-7541-482f-910d-46b3199063a
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1437033304
     places.history.expiration.transient_current_max_pages: 104858
     plugin.importedState: true
     print.printer_PDFCreator.print_bgcolor: false
     print.printer_PDFCreator.print_bgimages: false
     print.printer_PDFCreator.print_evenpages: true
     print.printer_PDFCreator.print_footercenter:
     print.printer_PDFCreator.print_footerleft: &PT
     print.printer_PDFCreator.print_footerright: &D
     print.printer_PDFCreator.print_headercenter:
     print.printer_PDFCreator.print_headerleft: &T
     print.printer_PDFCreator.print_headerright: &U
     print.printer_PDFCreator.print_in_color: true
     print.printer_PDFCreator.print_margin_bottom: 0.5
     print.printer_PDFCreator.print_margin_left: 0.5
     print.printer_PDFCreator.print_margin_right: 0.5
     print.printer_PDFCreator.print_margin_top: 0.5
     print.printer_PDFCreator.print_oddpages: true
     print.printer_PDFCreator.print_orientation: 0
     print.printer_PDFCreator.print_reversed: false
     print.printer_PDFCreator.print_scaling: 1.00
     print.printer_PDFCreator.print_shrink_to_fit: true
     privacy.donottrackheader.enabled: true
     security.disable_button.openCertManager: false

 Graphics

     Adapter Description: Intel(R) HD Graphics 3000
     Vendor ID: 0x8086
     Device ID: 0x0126
     Adapter RAM: Unknown
     Adapter Drivers: igdumd64 igd10umd64 igd10umd64 igdumd32 igd10umd32 igd10umd32
     Driver Version: 9.17.10.3347
     Driver Date: 1-29-2014
     Direct2D Enabled: true
     DirectWrite Enabled: true (6.2.9200.17292)
     ClearType Parameters: Gamma: 2200 Pixel Structure: R ClearType Level: 100 Enhanced Contrast: 300
     WebGL Renderer: false
     GPU Accelerated Windows: 3/3 Direct3D 11

     AzureCanvasBackend: direct2d 1.1
     AzureSkiaAccelerated: 0
     AzureFallbackCanvasBackend: cairo
     AzureContentBackend: direct2d 1.1

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.10.8
     4.10.8

     NSS
     3.19.2 Basic ECC
     3.19.2 Basic ECC

     NSS Util
     3.19.2
     3.19.2

     NSS SSL
     3.19.2 Basic ECC
     3.19.2 Basic ECC

     NSS S/MIME
     3.19.2 Basic ECC
     3.19.2 Basic ECC

check the error console on the Tools menu (alt+T) and see if there are errors about Diffie-Hellman

The console gives the following error. Timestamp: 17-07-2015 09:11:46 Error: mail.hclinsys.com : server does not support RFC 5746, see CVE-2009-3555

The mails were sent from thunderbird using the sameil mail server till i upgraded to the current version.

Regards

To diagnose your problems with Thunderbird, try the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

I have tried the same and found there is no issue with the laptop or windows versions. I have windows 7 64 bit.

I have downgraded to Thunderbird version 37.0 and the mails have started working.

Looks like a problems with the new release.

Please heck the error cons=ole with V38 for the error messages I discuss here. http://thunderbirdtweaks.blogspot.com.au/2015/07/logjam-and-thunderbird.html

Thanks a ton Matt, The problem of sending mails is resolved.