So, I am having another problem with Outlook 2019 (stand alone version, running on my desktop rather than Office 365):

I just added another email account to one of my mail servers. Everything appears to be correct. The test messages from Outlook are all going through, and it's confirming that they did indeed go through ... except they are not.

Despite the fact that Outlook seems to be satisfied with this result ... and the messages are appearing on my mail server as being sent from one of my other accounts and received by the new one ... they are not showing up in Outlook's Inbox. (They are appearing in Outlook's Sent box, however.)

I have checked and re-checked all the settings in the new account. They exactly match the settings in the only other account for that domain. The only differences are the email address name and the password.

No clue as to what the problem might be at this point. No error mesages of any kind from Outlook or my mail server. I'd welcome any suggestions on what to try next. Thanks.