Jarius,
I have tried all of your suggestions and learned a little in the process. Using IMAP instead of POP3 did not make any difference.
Even though I don't see how the browser could affect communication between the OUTLOOK.COM server and the VISI.COM servers, I did try using Chrome without any different results. I also cleared cookies and tried all options I tried before without success.
Here is what I learned, though. When I happened to try sending email with the VISI.COM address but using the OUTLOOK.COM server option, the problem disappeared and the account was connected. This is not really a good alternative, though, since the inconsistency
between the from address and the headers can increase the chance of a message being filtered out as junk from what I have read. It does seem to indicate that the problem is with the SMTP connection and not with the IMAP or POP3 connections. It should have
been possible for OUTLOOK.COM to have displayed something indicating this message was related to the SMTP connection, allowing concentration on the real source of the problem. Again, though, this isn't really a solution.
To repeat, the settings I have used on other email programs, including with OUTLOOK 2016, have continued to work as expected, including SMTP settings for VISI.com, and I have not changed these in some time.
I do not understand your suggestion that "You can also try to connect a different account first and try to add the VISI.com domain as a connected account instead in Outlook.com." Since I am logged into the OUTLOOK.COM website, I am logged into an OUTLOOK.COM
account and do not believe there is a way to connect another account without involving an OUTLOOK.COM account. If after all I am writing here, please help me understand this if you think this still seems to be worth pursuing.
I know a little of my own frustration is showing here, and I do not mean to take it out on you. However, when reading in other forums, I see that similar problems to mine have been regularly reported with the new OUTLOOK.COM migration and there is now another
person here experiencing something like this. Further, it came up in the OUTLOOK.COM preview phase as well, and when following through the threads, Microsoft generally asked to be contacted privately and the threads died without explanation. I only read
those preview messages and was not part of the preview program. It seems likely that someone in the OUTLOOK.COM sphere knows why something that worked but has stopped working with at least some SMTP servers since the migration has occurred. I don't want
to spend time trying to make something work that is known not to work. I have appeared to have done just that with my experimenting with POP3 and IMAP, although I assume your best intentions in having me try that. Surely the error code in the subject of
this conversation has a specific meaning to people that understand these types of protocols that might allow me to ask the right questions of my email provider.
In addition, the "Send Only" option remains available, but I learned only by digging that this option no longer works. I can work around this option not being available, but what is upsetting is that it remains an option and that Microsoft has not generally
indicated that it does not work. The option should be removed or a warning that it is temporarily unavailable should be right on the web page. I do appreciate the fact that you have taken the time to look into this and have confirmed this is the case, though.
Further, the fact that you have taken time to tried to address my concerns is very much appreciated. Would you do what you can to get clarification from the appropriate places in Microsoft as to what might be happening?