Could you please see if you have configured your SMTP server according to the recommended settings?

SMTP

   Server Name: smtp.gmail.com
   Port: 587 (you could also use port 25 if your ISP doesn't block it)
   Username: Your FULL email address
   Secure connection: STARTTLS
   Secure authentication: normal password 

Don't configure Thunderbird to save a copy of any messages you send in tools -> account settings -> copies & folders. Gmail's SMTP server automatically saves a copy of any message you send in the Sent Items folder for you.

The SMTP server also supports using port 465 with SSL/TLS.

Hi Sander,

Thank you very much for your help. I did everything you suggested but the same thing is still happening. Do you have any other suggestions?

Thanks, Greg

https://support.mozilla.org/en-US/kb/cannot-send-messages

Thanks christ1, but none of the information on that page helped. Any other ideas? In case it helps, I've attached a screenshot of my server settings.

Did you reset the password Thunderbird has remembered?

Did Thunderbird prompt you for the password after that when trying to send mail?

Connection Security SSL/TLS, Port 465 works for me for smtp.gmail.com.

The only password I can think of that Thunderbird wants is my Gmail password, which I have not changed ever. Thunderbird starting asking me for a password seemingly out of the blue.

I tried changing my connection security to SSL/TLS and my port to 465 but I am still having the same problem.

If anyone can think of anything else that could be causing the problem, please let me know. Thanks!

Try to reset the password Thunderbird has remembered.

http://kb.mozillazine.org/Setting_and_changing_email_passwords

Thanks christ1, but no luck. I changed my Gmail password and tried entering the new password when Thunderbird asked me for it, but it did not work.

What error did your get?

Can you post your Troubleshooting Information?

Help (Alt-H) - Troubleshooting Information

I have added two screenshots. The first one shows Thunderbird asking me for a password. The second one shows the error I get when I enter my password.

Your Troubleshooting Information?

I'm sorry but I don't know what you mean by Troubleshooting information. I've outlined everything I have tried here in the thread. What information exactly do you want?

Help (Alt-H) - Troubleshooting Information

Copy the information and paste it into your reply.

Ok, is this what you/re looking for?

Application Basics

Name: Firefox Version: 29.0.1 User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0

Crash Reports for the Last 3 Days

All Crash Reports (including 3 pending crashes in the given time range)

Extensions

Name: AVG Security Toolbar Version: 18.1.0.443 Enabled: false ID: avg@toolbar

Name: Norton Toolbar Version: 2013.4.10.12 Enabled: false ID: {2D3F3651-74B9-4795-BDEC-6DA2F431CB62}

Name: Norton Vulnerability Protection Version: 12.2.0.5 - 1 Enabled: false ID: {BBDA0591-3099-440a-AA10-41764D9DB4DB}

Name: OneClick YouTube Downloader Version: 1.0.8 Enabled: false ID: {35379F86-8CCB-4724-AE33-4278DE266C70}

Name: RealDownloader Version: 1.3.3 Enabled: false ID: {DF153AFF-6948-45d7-AC98-4FC4AF8A08E2}

Important Modified Preferences

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 browser.places.smartBookmarksVersion: 6 browser.search.suggest.enabled: false browser.search.useDBForOrder: true browser.sessionstore.upgradeBackup.latestBuildID: 20140506152807 browser.startup.homepage: about:home browser.startup.homepage_override.buildID: 20140506152807 browser.startup.homepage_override.mstone: 29.0.1 dom.mozApps.used: true dom.w3c_touch_events.expose: false extensions.lastAppVersion: 29.0.1 gfx.direct3d.last_used_feature_level_idx: 0 gfx.direct3d.prefer_10_1: true network.cookie.prefsMigrated: true places.database.lastMaintenance: 1400052586 places.history.expiration.transient_current_max_pages: 104858 plugin.disable_full_page_plugin_for_types: video/x-ms-wmv,audio/x-ms-wma,application/x-mplayer2,video/x-ms-asf,video/x-ms-asf-plugin,video/x-ms-wvx,application/pdf plugin.importedState: true print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_bgcolor: false print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_bgimages: false print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_colorspace: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_command: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_downloadfonts: false print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_duplex: -935357122 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_edge_bottom: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_edge_left: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_edge_right: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_edge_top: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_evenpages: true print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_footercenter: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_footerleft: &PT print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_footerright: &D print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_headercenter: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_headerleft: &T print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_headerright: &U print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_in_color: true print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_margin_bottom: 0.5 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_margin_left: 0.5 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_margin_right: 0.5 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_margin_top: 0.5 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_oddpages: true print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_orientation: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_page_delay: 50 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_data: 1 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_height: 11.00 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_name: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_size_type: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_size_unit: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_paper_width: 8.50 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_plex_name: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_resolution: 136571536 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_resolution_name: print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_reversed: false print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_scaling: 1.00 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_shrink_to_fit: true print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_to_file: false print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_unwriteable_margin_bottom: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_unwriteable_margin_left: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_unwriteable_margin_right: 0 print.printer_chainsaw_(HP_LaserJet_400_colorMFP_M475dw).print_unwriteable_margin_top: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_bgcolor: false print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_bgimages: false print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_colorspace: print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_command: print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_downloadfonts: false print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_duplex: -935357122 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_edge_bottom: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_edge_left: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_edge_right: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_edge_top: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_evenpages: true print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_in_color: true print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_margin_bottom: 0.5 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_margin_left: 0.5 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_margin_right: 0.5 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_margin_top: 0.5 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_oddpages: true print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_orientation: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_page_delay: 50 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_data: 1 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_height: 11.00 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_name: print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_size_type: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_size_unit: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_paper_width: 8.50 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_plex_name: print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_resolution: 136571536 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_resolution_name: print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_reversed: false print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_scaling: 1.00 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_shrink_to_fit: true print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_to_file: false print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_unwriteable_margin_bottom: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_unwriteable_margin_left: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_unwriteable_margin_right: 0 print.printer_Epson_Stylus_COLOR_740_ESC/P_2_(Copy_2).print_unwriteable_margin_top: 0 privacy.cpd.cookies: false privacy.cpd.offlineApps: true privacy.cpd.sessions: false privacy.sanitize.migrateFx3Prefs: true privacy.sanitize.timeSpan: 0 security.warn_viewing_mixed: false storage.vacuum.last.index: 1 storage.vacuum.last.places.sqlite: 1398333116

Graphics

Adapter Description: Intel(R) HD Graphics Family Adapter Drivers: igdumd64 igd10umd64 igd10umd64 igdumdx32 igd10umd32 igd10umd32 Adapter RAM: Unknown Device ID: 0x0126 Direct2D Enabled: true DirectWrite Enabled: true (6.2.9200.16571) Driver Date: 7-19-2011 Driver Version: 8.15.10.2455 GPU #2 Active: false GPU Accelerated Windows: 2/2 Direct3D 10 Vendor ID: 0x8086 WebGL Renderer: Google Inc. -- ANGLE (Intel(R) HD Graphics Family Direct3D9Ex vs_3_0 ps_3_0) windowLayerManagerRemote: false AzureCanvasBackend: direct2d AzureContentBackend: direct2d AzureFallbackCanvasBackend: cairo AzureSkiaAccelerated: 0

JavaScript

Incremental GC: true

Accessibility

Activated: false Prevent Accessibility: 0

Library Versions

NSPR Expected minimum version: 4.10.3 Version in use: 4.10.3

NSS Expected minimum version: 3.16 Basic ECC Version in use: 3.16 Basic ECC

NSSSMIME Expected minimum version: 3.16 Basic ECC Version in use: 3.16 Basic ECC

NSSSSL Expected minimum version: 3.16 Basic ECC Version in use: 3.16 Basic ECC

NSSUTIL Expected minimum version: 3.16 Version in use: 3.16

Almost. It would be great if you could provide the information for Thunderbird.

When I open Thunderbird and press Alt-H it goes to the Help drop down menu but I don't see a Troubleshooting Information option.

What version of Thunderbird are you running?

24.5.0

Troubleshooting Information is the second item in the Help menu using TB 24.5.0 for Windows.

Can you provide a screenshot of your Help menu?

http://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem

I've included a screenshot of my TB help menu. As you can see, there is no Troubleshooting Information option.