Get an alias address in the sender's field in Gmail

Let's say I have two Google accounts: Y

I'm connected to Gmail in my perso account. I have added Pro as an alias address to send mail as, in the Gmail settings (Settings> Accounts and Import> Send mail as).

But, when I select the Address when sending an email, some of my contacts sometimes still see the original, address. And when checking the raw message, it seems, it is still used in the Sender: field; it is only present in the Since: field.

How to do it so that the people to whom I send the mail. Never see the address I tried to mark and unmark "Treat as an alias" in the Gmail settings, but this did not change.