Do you have multiple accounts? The error suggests you're trying to send from account A through the smtp that has account B's User Name (email address). Either that, or the setting for the smtp is wrong. Spectrum suggests using mail.twc.com, port 587, STARTTLS, normal password, User Name = email address.

Thanks for responding. I've had 3 email addresses in the same domain and could email from one address to another with no problem. Now outgoing email from either account doesn't go through. The domain names twc.com, roadrunner.com and maine.rr.com could always be used interchangeably.

Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) maine.rr.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again.

The question remains: do you have the accounts matched with the correct smtp servers?

See https://support.mozilla.org/en-US/questions/1350593

The fact the various servers could be used interchangeably in the past probably doesn't apply if Spectrum has changed the server configuration or authentication requirements.

When I contacted Spectrum, they asked me to test webmail and, since it worked fine, to contact Thunderbird support. They don't offer support for any mail clients.

They're abdicating their responsibility, but that's irrelevant here. What sfhowes is telling you is that you need a unique smtp server for each account. And I encourage you to use password if that is their suggestion.

Thanks for responding. I've had 3 email addresses in the same domain (maine.rr.com) and could email from one address to another with no problem. Now outgoing email from either account doesn't go through. The domain names twc.com, roadrunner.com and maine.rr.com could always be used interchangeably.

Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) maine.rr.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again.

Do SMTP parameters always have to have "smtp" in it, as in smtp-mail.twc.com? BTW, Spectrum that acquired Tim Warner Cable a few years ago claimed of having never heard of SMTP.

Time Warner Cable (twc). They told me recently that twc is still good. Also, I've never used passwords for outgoing mail.

Do you have separate SMTP servers for each account? That has been asked (with no response) and seems close to the issue that the error message is referring to. And if you have separate servers defined, are they attached to the right account? If not sure, we can assist in verifying that. The fundamental issue from your initial post is that you're sending mail from account A for message from account b. That needs to be clarified. And many email providers are now requiring more security in their connections, so just because you didn't need passwords in the past, does not mean that you don't need them now.

I've never had separate SMTP servers for these 3 accounts. Now I can't send email from either of these 3 accounts to an outside account, nor just between the 3 accounts. There's a chance that I incorrectly named SMTP servers. That was the reason I asked if "smtp: has to be a part of the SMTP server's name, as in smtp-mail.twc.com or smtp-twc.com.

Spectrum could't tell me what their SMTP server's name was. (They didn't know what SMTP stood for.) In response to my call to their techsupport, they sent me a single page that listed the 587 port and, under Required Authentication - Yes, or checked. (Mine has always been set as none).

So now I feel lost and don't know what else to try.

Spectrum uses many different server names, but I did find this one with a web search: https://webmail.spectrum.net/index.php/mobile You might ask each tech support group for setting to set up a phone. The settings would be the same.

Spectrum asked me to check if I could receive and send email via webmail.spectrum net. Once I told them I could, they told me that's where their support ends, and I should work my problem out with app support, i.e. TB.

All 3 TB mail addresses on my phone work just fine.

The settings on phone are probably the same ones to apply on PC.

On the phone, all 3 accounts have SMRP server mail.twc.com. Port 587. Security type STARTTLS.

In TB, do SMTP server names have to contain smtp?

I've never had separate SMTP servers for these 3 accounts. Now I can't send email from either of these 3 accounts to an outside account, nor just between the 3 accounts. There's a chance that I incorrectly named SMTP servers. That was the reason I asked if "smtp: has to be a part of the SMTP server's name, as in smtp-mail.twc.com or smtp-twc.com.

Ok, as you can see from the information below, all those servers are unique with it's own IP address. It is irrelevant what you did in the past, they are not "interchangable"

Pinging twc.com [142.136.168.7] with 32 bytes of data:
Pinging roadrunner.com [71.74.186.228] with 32 bytes of data:
Pinging maine.rr.com [24.39.55.158] with 32 bytes of data:
Pinging mail.twc.com [47.43.26.4] with 32 bytes of data:

Now I have "picked" the mobile settings page at spectrum. https://www.spectrum.net/support/internet/mobile-email-setup have a look, the very first thing it says is that the user name is "Your full Spectrum-provided email address". The error you are getting is the server you are trying to use required that the from address and the username must match. It is that simple.

Go to outgoing servers (SMTP) in account settings and look at your list of outgoing servers. Do you have one for each email address? If not you need to add some. I suggest you use the email address as the name as it makes identifying which you want to be using much simpler. The settings for each outgoing server will probably be identical, only varying in username and account name. (Note the account name is just a convenience for you to make sorting out which is which easier. It has no intrinsic value beyond making a human relatable name)

Once you have your outgoing servers set up, that will be however many (three?) identical SMTP server entries only varying in name and username. Go to the account settings for each of your incoming account. At the bottom of the first page of entries for each account is the chosen SMTP server entry for that account. Pick the correct one (that is where naming them with the email address makes it simple) and move to the next account until all have their own correct outgoing server set.

Now you should be good to go.

No, the smtp server name may vary. Use the names that you use on your phone.

I'm asking if the word "smtp" should be a part of the SMTP server's name? As in smtp-mail.twc.com or just mail.twc.com?

I'm asking if the word "smtp" should be a part of the SMTP server's name? As in smtp-mail.twc.com or just mail.twc.com?

The server name should be whatever your email provider tells you to use. In your case the correct details are on the spectrum web site and I linked to them in my post. https://support.mozilla.org/en-US/questions/1430461#answer-1617460

You use what they say you use, or expect it to not work.

Just mail.twc.com

Guys,

I use the same SMTP server (mail.twc.com) for all 3 addresses. If my email addresses end on maine.rr.com, do I have to use the mail.maine.rr.com server?

Are you saying that user names in the SMTP configuration should be a full email address, not just a username?

If so, I don't see how it can be entered in the SMTP server.