So, what does your business domain provider suggest you do? Presumably he hosts your email accounts?

The business domain host is aware, as I am, that any and all customers of Time Warner/Spectrum are required to use TWC/Spectrum's SMTP settings for Outgoing email. My business domain host insists that only TWC/Spectrum can resolve the issue. I have spoken for over 2 hours with TWC/Spectrum and they have been entirely unable to resolve the issue. They, in turn, insist that the issue lies with Thunderbird. And given the very large number of questions on this forum that are related specifically to an inability to Send emails using Thunderbird, and related even more specifically to Thunderbird not being able to access the user's ISP (password issues, timed out connection, etc), I am strongly inclined to believe that the problem lies with Thunderbird itself. I need a solution. The issue is costing me money.

When I had a similar situation with my own domain, and using email accounts attached to that domain, the answer was (then) to use my ISP's SMTP server.

To all intents and purposes, the messages appeared to my correspondents as having been sent "from" the domain email address and not the ISP's address. True, an inquisitive person could have examined the headers and discovered the actual origin. But since very few of us actually own and run our own servers, and in fact use some third party's system, almost all email is actually sent by a proxy.

This was a few years ago and since then standards have evolved. My webhost upped his game and set up his own smtp server for his clients to use. My ISP also tightened up and started to refuse email messages sent using another domain in the "from" address. This practice is now the norm.

It's possible (probable?) that your ISP is doing the same, though if so, it is shameful that they haven't been able to tell you this. I'd say your webhost is behind the times, expecting you to rely on other parties to support your sending.

If you think this is specifically a Thunderbird problem (and I don't think it is) you can prove it by setting up this account in another email client and demonstrate it working there.

If your webhost refuses to provide the smtp server, and your ISP refuses messages sent using your business domain, then you need to find an alternative smtp server that will process them (or switch either webhost or ISP.) I believe that both googlemail and gmx email accounts can do the smtp for you, though you would have to add the business address to these accounts to allow them to handle it for you.

Thank you for the advice, Zenos. I ultimately resolved the issue by returning the new Dell AIO to the store and reverting to my old computer, and thus my former email software (after considerable sleuthing, it turns out that the monitor flashing on and off was nothing more than a faulty surge protector!). My webhost does not have its own SMTP servers. And Spectrum/TimeWarner swears that they are not blocking my outgoing email. One of the reasons that lead me to think that it IS an issue with Thunderbird is that my outgoing email works perfectly when I revert to my old software (Windows Live Mail) using exactly the same SMTP settings that I used with Thunderbird). I have no idea how I would find an alternate SMTP server, if the problem were continuing. And I cannot switch ISP, since Spectrum/TimeWarner effectively enjoys a total monopoly in my region. It's them or Frontier copper phone lines at a snail's pace maximum of 6 mbps! No other companies currently serve the Palm Springs area. Anyway, replacing the surge protector and reverting back to my old computer with Windows 7 and Windows Live Mail solved everything.

So you are now living with a device that is probably about to fail due to old age using software that is not supported by anyone at all. I would not call that a solution.

My guess is you are foul of the free anti virus the good people at dell installed on your computer for you. OR the one you installed provided by your ISP. Anti virus products are notorious for causing connectivity issues with mail servers.

Another common cause of trouble when moving from long unsupported software to new are the cyphers used in SSL and TLS connections. Live has not been updated for years Thunderbird is updated every 6 weeks, so mail servers must use current security to connect to Thunderbird.

Perhaps if you were to post the server details we could test them to see if they are up to snuff. Or you could go here and do it yourself. The domains entry on that site requires a : and a port number to test correctly.

I turned to this forum only with extreme reluctance and only because Mozilla does not have live human customer support. Your response, Matt, is a perfect example of why I avoid forums: your first statement is an unsympathetic criticism of my decision and not at all helpful.

I had already disabled all of the anti-virus software that I could locate using the Windows 10 program directory (or whatever you call it) ... itself a very difficult process if the user is not significantly experienced with Windows 10. That did not help. I did *not* myself add any additional security software.

The mail server configurations that I was using were current, according to the third tier technical support people at Spectrum/Time Warner. I have no way to know otherwise. And again, S/TWC *REQUIRES* me to use THEIR SMTP servers, full stop. So I am at their mercy.

Thank you for taking the time to attempt to respond to my query. But as I said, I ditched the new computer and Mozilla Thunderbird, and now my email works just fine ... using S/TWC's SMTP servers.

JadeLane said

I turned to this forum only with extreme reluctance and only because Mozilla does not have live human customer support. Your response, Matt, is a perfect example of why I avoid forums: your first statement is an unsympathetic criticism of my decision and not at all helpful.

It was not meant to be helpful in terms of your inability to send mail. You apparently had found a solution you were happy with.

It was meant to draw your attention to the fact that your solution is a stop gap as best. A disaster waiting to happen at worst. Not a solution at all really, just a short term workaround.

You bough a new device and stopped using it and reverted to something your had replaced. I assumed you replaced it for a reason. My apologies if you simple bought a new device because you wanted one.

Windows live mail is no longer supported by Microsoft. Regardless of my opinion that makes it dangerous to use and not appropriate in a business at all. Business and product liability issues appear as soon as you use unsupported software. There are also issues that a lot of this old software (including prior versions of Thunderbird) can not continue to connect to mail servers.

Just as an aside. Google users do not use time warners SMTP servers, and neither should anyone else. There are better more correct ways.

Perhaps this discussion from 2004 were folk were complaining TWC requires you to use their server will shed some light. http://www.dslreports.com/forum/r20740159-TWC-SMTP-Port-587-Blocked-Now

TWC/road runner have been blocking outgoing mail port 25 for decades on domestic DSL because port 25 is used by servers to send mail not mail clients. But you are not running a mail server, so should not be using port 25. Or are you? Back in the 1990s port 25 was a common outgoing port for mail clients. I suspect thy also still allow you to connect to their mail server with it. It would reduce the number of support calls. It might even support your assertion that tier three said you had to use their server. I have nothing else.