Try smtpauth.mail.wowway.com on 587, connection security = none, authentication = password, transmitted insecurely, User Name = email address.

https://www.wowway.com/docs/wow/documents-support-internet/pop-imap-settings.pdf?sfvrsn=78ffdfaf_6

See also : https://support.mozilla.org/en-US/questions/1316575

Thank you for suggestions sfhowes. I tried smtpauth.mail.wowway.com on 587, connection security = none, authentication = password, transmitted insecurely, User Name = email address. however still achieve the same results as before, that is, sometimes email will go through first try, other times the send message error displays and it fails. The one difference with using those settings is that it prompts for the password when attempting to send the message. Is that setting intended to be for test purposes only? The reason I ask is those settings don't appear to secure the password. Unless there is something I don't understand. Thanks for link re eset node32 antivirus being possible culprit. Although I did completely uninstall eset Internet Security and ran tests but still encountered the send message error.

So at the moment I am still stumped about what is causing that problem and how to resolve.

I used Thunderbird for about a year or more without this type of problem. I don't know if it started after a new release came out or what event may have triggered this problem starting. I don't think any settings changed with my email provider, WOW, as far as I know. I know I changed my password one time for some reason, which I don't recall.

If you are prompted for a password after changing the smtp settings, there should be a checkbox in the prompt to save the password in Saved Passwords in TB Options/Privacy & Security. Check that there are no obsolete passwords in Saved Passwords.

If the problem is due to an unreliable WOW server, you might consider adding an account with e.g. gmail or outlook.com and using its smtp server to send from the WOW account. If the WOW account is added as a registered sender on the gmail or outlook website, your WOW account will appear as the sending address to recipients, even though mail is sent through a non-WOW (and secure) server.

I tried it again, with those changes ( smtpauth.mail.wowway.com on 587, connection security = none, authentication = password, transmitted insecurely, User Name = email address, and then specified to save the password.) So far so good, it seems to have solved the problem! I'll give it more time and tests to know for sure, since it has been a flaky on and off problem, but initial indications are that it is working the way it should, with no 'send message errors.'

1) Just to confirm, should I stick with those settings, even though the settings "connection security = none, authentication = password, transmitted insecurely" don't sound like that is secure?

By the way, there were no obsolete passwords in Saved Passwords.

2) Regarding "If the problem is due to an unreliable WOW server..." how would I know that is the cause. Is there a way to determine that?

3) A follow on about the suggestion of adding my WOW account as a registered account on gmail, to send via gmail's smtp server while showing my WOW email address, could that be a way to drop WOW in the future but still retain my WOW email address? (I think I am attached to WOW long term if I want to keep my WOW email address, unlike someone being able to move their phone number from carrier to carrier.)

oh-oh, further to above, I am getting the 'send message error' again. Back to the drawing board.....

The main disadvantage of no connection security is that you probably can't connect if you're not on the WOW network, e.g. with a mobile device.

I don't know how to diagnose the WOW network, except try an account with known settings such as gmail. If gmail doesn't work, and you've removed ESET, I would suspect it's due to the WOW network.

You could keep your WOW address and receive mail on the incoming WOW server, but send on the gmail smtp.

Thank you for that insight. Mobile access is not important, and even if using WOW email on a mobile device that can be done with WOW web mail and I don't think there is a problem with that, the problem is with using Thunderbird as email client.

I'm not sure how to diagnose the WOW network either, other than maybe the way you suggested. Their frontline support isn't that knowledgeable, and their back end support, who the front line support hands it off to isn't that responsive, in my experience.

I have used WOW for many years for email, with several clients, such as Outlook Express, Windows Live Mail, and now for about a year and half Thunderbird, but only recently has this issue been a problem.

The tech support for the company where I purchased my laptop and eset antivirus had suggested deleting and reinstalling Thunderbird as a possible next step, last night when I called them. However I don't want to lose my email messages and would want to make sure I'd be able to restore them if deleting and reinstalling Thunderbird, so I'm not sure if that is a good recommendation or not.

Reinstalling the program doesn't affect the user data in the separate profile folder, but it also doesn't often fix problems that are due to issues with the profile.

Thank you for the explanations. Today I received a reply from WOW tech support that advises the same settings as you suggested. I have tried those again, although still getting the 'send message error' at times. I will keep working on it to see if there is something I am missing.

Prior to the WOW email instructions explaining the settings, (which are the same as in the link you posted above) they said "Please make sure your settings are as follows : as long as you are on the WOW internet network (not on a non wow internet network such as a hotel)"

I'll ask them about this--since I don't understand it. In other words I mostly use the laptop with Thunderbird at home and connected to my ISP's (WOW) connection, but at times if traveling I may use it at a hotel or at a relative's house connected to their ISP. Therefore in light of that statement from WOW "as long as you are on the WOW internet network..." I wonder if the settings need to be different when traveling, since I am not on the WOW internet network in those circumstances, if I understand correctly.

As mentioned above, you may not be able to make a non-secure connection to the WOW smtp server if you're on a non-WOW network.