Get rid of Norton if you want things to run at full speed all the time.

Try it by restarting your operating system in safe mode with networking.

Uninstalled Norton 360, restarted W10 in safe mode with networking, sent Test in subject field only, timed out after 32 seconds, sent same message, took 25 seconds to send. Restarted Thunderbird in safe mode w/disable all add-ons, sent same message, sent it instantly, sent same message again, took 26 seconds. 90% of the time it takes around 25 seconds to send an email and the other 10% it sends instantly or it times out. Re-installed Norton 360, restarted both W10 & Thunderbird in normal mode. What's next?

25 seconds to talk to a busy server. Is that what this discussion is about? That is really not very slow as the process is from connecting and asking the server to send your mail to the server saying it has sent the mail. This is different from many mail clients which just drop the mail into an outbox and send it later whenever that is.

However timeouts are not much fun, you could log the sending of the mail and see if that shows anything significant. https://thunderbirdtweaks.blogspot.com/2021/10/logging-mail-sending-in-thunderbird.html

I followed the instructions per the above link but I don't have a clue as to what I'm looking at.

window.controllers/Controllers is deprecated. Do not use it for UA detection. blank NS_ERROR_FAILURE: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIAutoCompleteInput.popup] LoginManagerChild.jsm:194 mailnews.smtp: Sending message <8138bfe0-7d9c-5cb5-9c6d-736e9840d1bd@atmc.net> SmtpService.jsm:84:18 mailnews.smtp: Connected SmtpClient.jsm:385:17 mailnews.smtp: S: 220 2.0.0 mail.informnet.com ESMTP ecelerity 4.3.1.69410 r(Core:4.3.1.0) Mon, 22 Nov 2021 17:40:12 -0500

SmtpClient.jsm:411:17 mailnews.smtp: C: EHLO [192.168.0.6] SmtpClient.jsm:577:19 mailnews.smtp: S: 250-smtp02.nrtc.email-ash1.sync.lan says EHLO to 70.35.188.23:51353

250-STARTTLS

250-ENHANCEDSTATUSCODES

250-PIPELINING

250-8BITMIME

250-AUTH=LOGIN

250-AUTH LOGIN

250 XDUMPCONTEXT

SmtpClient.jsm:411:17 mailnews.smtp: Possible auth methods: LOGIN SmtpClient.jsm:897:17 mailnews.smtp: Current auth method: LOGIN SmtpClient.jsm:615:17 mailnews.smtp: Authentication via AUTH LOGIN SmtpClient.jsm:623:21 mailnews.smtp: C: AUTH LOGIN SmtpClient.jsm:577:19 mailnews.smtp: S: 334 VXNlcm5hbWU6

SmtpClient.jsm:411:17 mailnews.smtp: AUTH LOGIN USER successful SmtpClient.jsm:959:17 mailnews.smtp: C: Logging suppressed (it probably contained auth information) SmtpClient.jsm:573:19 mailnews.smtp: S: 334 UGFzc3dvcmQ6

SmtpClient.jsm:411:17 mailnews.smtp: AUTH LOGIN PASS successful SmtpClient.jsm:974:17 mailnews.smtp: C: Logging suppressed (it probably contained auth information) SmtpClient.jsm:573:19 mailnews.smtp: S: 235 2.0.0 Authed. Go on.

SmtpClient.jsm:411:17 mailnews.smtp: Authentication successful. SmtpClient.jsm:1087:17 mailnews.smtp: C: MAIL FROM:<rblank1@atmc.net> BODY=8BITMIME SmtpClient.jsm:577:19 mailnews.smtp: S: 250 SPF validation soft failure

SmtpClient.jsm:411:17 mailnews.smtp: MAIL FROM successful, proceeding with 1 recipients SmtpClient.jsm:1121:17 mailnews.smtp: Adding recipient... SmtpClient.jsm:1126:17 mailnews.smtp: C: RCPT TO:<rblank1@atmc.net> SmtpClient.jsm:577:19 mailnews.smtp: S: 250 2.1.5 Accepted for you

SmtpClient.jsm:411:17 mailnews.smtp: RCPT TO done, proceeding with payload SmtpClient.jsm:1186:19 mailnews.smtp: C: DATA SmtpClient.jsm:577:19 mailnews.smtp: S: 354 3.0.0 continue. finished with "\r\n.\r\n"

SmtpClient.jsm:411:17 mailnews.smtp: Sending 422 bytes of payload SmtpClient.jsm:547:17 mailnews.smtp: S: 250 2.0.0 OK F0/60-04045-B6C1C916

SmtpClient.jsm:411:17 mailnews.smtp: Message sent successfully. SmtpClient.jsm:1245:21 mailnews.smtp: C: QUIT SmtpClient.jsm:577:19 mailnews.smtp: Socket closed. SmtpClient.jsm:485:17 mailnews.smtp: S: 221 2.3.0 smtp02.nrtc.email-ash1.sync.lan closing connection

SmtpClient.jsm:411:17 mailnews.smtp: Closing connection... SmtpClient.jsm:151:17