IanMosley is closer, but... when i firstly started Outlook 2019, it begins with some configuration wizard and didn't allow me to do anything else. See first screenshot - it is one part of this.
And that is the problem - it allows set only email address, not username. This configuration wizard is unusable for me and without finishing it, Outlook 2019 did not continue further.
Attachment 221823
Yes, i already got it. I can use virtual users and maintain another database (or table in textfile) of this alternative usernames (in other word aliases) for my MTA. Fine, but i really don't want to do it just because only one MUA from many needs it.
If only one application need something unusual without really good reason i must consider it error. Ok?
But fortunatelly, there is way around.
As i linked before, i can run Outlook 2019 with parameter
"outlook.exe /manageprofiles". It will start similar dialog to one IanMosley uploaded.
It looks little retro, it is little chaotic, but it allows set everything i needs, especially username.
Attachment 221824
Thanks again, even if we did not understand each other exactly.
Now, problem is solved.