Ciao Giancarlo, OK. Let it be. I'll create a new account for that. But wonder whether my old one will be purged somewhen and I will be able to use my old username? - If it is non-active for a long period of time, why to keep it anyway? But, of course, I understand that there is no way to prove its privacy though.
I don't think there is much help for you. With no access to your old mailbox, there is no way for you to proving ownership to it, there is? My suggestion is, don't overthink this and create a new account. If you're worried about packages you've owned, if they weren't uploaded yet to AUR4, you can regain their ownership by simply creating then again on it. If you're worried about comments, then it's pretty much game over.
Cheers, Giancarlo Razzolini
-- Kind regards, Radislav (Radicchio) Golubtsov