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.

Please indicate which one is the troubled account.

Application Basics

   Name: Thunderbird
   Version: 52.1.1
   User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.1.1
   Profile Folder: Show in Finder
   Application Build ID: 20170509142926
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.googlemail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.googlemail.com:465, SSL, passwordCleartext, true

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

   account3:
     INCOMING: account3, , (pop3) inbound.att.net:995, SSL, passwordCleartext
     OUTGOING: , outbound.att.net:465, SSL, passwordCleartext, true

   account6:
     INCOMING: account6, , (imap) imap.mail.me.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.mail.me.com:587, alwaysSTARTTLS, passwordCleartext, true

   account7:
     INCOMING: account7, , (imap) imap.mail.me.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.mail.me.com:587, alwaysSTARTTLS, passwordCleartext, true

   account9:
     INCOMING: account9, , (pop3) inbound.att.net:995, SSL, passwordCleartext
     OUTGOING: , outbound.att.net:465, SSL, passwordCleartext, true

   account10:
     INCOMING: account10, , (pop3) inbound.att.net:995, SSL, passwordCleartext
     OUTGOING: , outbound.att.net:465, SSL, passwordCleartext, true

   account11:
     INCOMING: account11, , (imap) imap-mail.outlook.com:993, SSL, passwordCleartext
     OUTGOING: , smtp-mail.outlook.com:587, alwaysSTARTTLS, passwordCleartext, true

   account12:
     INCOMING: account12, , (imap) imap.gmail.com:993, SSL, OAuth2
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

   account13:
     INCOMING: account13, , (imap) imap.gmail.com:993, SSL, OAuth2
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

   account14:
     INCOMING: account14, , (imap) imap.gmail.com:993, SSL, OAuth2
     OUTGOING: , smtp.gmail.com:465, SSL, OAuth2, true

 Crash Reports

 Extensions
   ExQuilla for Microsoft Exchange, 52.2.1188, true, exquilla@mesquilla.com
   Lightning, 5.4.1.1, true, {e2fda1a4-762b-4020-b5ad-a41df1933103}
   Manually sort folders, 1.1.1, true, tbsortfolders@xulforum.org
   Quick Folder Move, 1.2, true, quickmove@mozilla.kewis.ch

 Important Modified Preferences

   Name: Value

     accessibility.typeaheadfind.flashBar: 0
     browser.cache.disk.capacity: 358400
     browser.cache.disk.filesystem_reported: 1
     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
     extensions.lastAppVersion: 52.1.1
     font.internaluseonly.changed: true
     mail.openMessageBehavior.version: 1
     mail.spotlight.firstRunDone: true
     mailnews.database.global.datastore.id: 8d8c791a-b14b-2c45-989a-e7b3d12a059
     mailnews.database.global.views.conversation.columns: {"threadCol":{"visible":true,"ordinal":"1"},"flaggedCol":{"visible":true,"ordinal":"3"},"attachmentCol":{"visible":false…
     media.gmp.storage.version.observed: 1
     network.cookie.prefsMigrated: true
     network.predictor.cleaned-up: true
     places.database.lastMaintenance: 1496511251
     places.history.expiration.transient_current_max_pages: 122334
     plugin.importedState: true
     print.macosx.pagesetup-2: PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPCFET0NUWVBFIHBsaXN0IFBVQkxJQyAiLS8vQXBwbGUvL0RURCBQTElTVCAxLjAvL0VO…
     security.sandbox.content.tempDirSuffix: {3b1550d5-8511-c144-82e9-d1c3a917f708}

 Graphics

     GPU #1
     Vendor ID: 0x10de
     Device ID: 0x119e

     Features
     WebGL Renderer: NVIDIA Corporation -- NVIDIA GeForce GTX 780M OpenGL Engine -- 2.1 NVIDIA-10.17.5 355.10.05.45f01

     AzureCanvasBackend: skia
     AzureCanvasAccelerated: 0
     AzureFallbackCanvasBackend: none
     AzureContentBackend: skia
     TileHeight: 1024
     TileWidth: 1024

 JavaScript

 Incremental GC: 1

 Accessibility

   Activated: 0
   Prevent Accessibility: 0

 Library Versions

     Expected minimum version
     Version in use

     NSPR
     4.13.1
     4.13.1

     NSS
     3.28.4
     3.28.4

     NSS Util
     3.28.4
     3.28.4

     NSS SSL
     3.28.4
     3.28.4

     NSS S/MIME
     3.28.4
     3.28.4

use this link http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac

Now you understand the menu differences, use that to convert what you found for Windows to your mac.

Or right click the account in the folder pane n the left and select settings. Then select server settings in the account settings dialog

I went to that location and the setting to change to OAuth2. Which I don't need because if you would look at the Troubleshooting Information I posted, all of the gmail accounts have this already set. Two of the accounts work, the third one doesn't.

Gmail accounts 12, 13, and 14 are already set to OAuth2 authentication.

account1: INCOMING: account1, , (imap) imap.googlemail.com:993, SSL, passwordCleartext OUTGOING: , smtp.googlemail.com:465, SSL, passwordCleartext, true

There's one Gmail account which has not.

I don't need because if you would look at the Troubleshooting Information I posted, all of the gmail accounts have this already set.

Interesting statement. See above.

Two of the accounts work, the third one doesn't.

As per your Troubleshooting Information there are 4 Gmail accounts.

I am wrong. There are 4 gmail accounts. The attached is what I get in Advanced.. for Server Settings for the gmail account with the issue.

I found where to set OAuth2. It's on the main page of Server Settings for Thunderbird on Mac.

I thought this was fixed. I'm able to receive email on this account. I'm unable to send emails on this account.

What other setting is needed to fix this issue?

All your outgoing (SMTP) settings are gathered together at the bottom of the list of accounts in Account Settings.