In the meantime, I have lost possession of the email address I have used to create my Poloniex account. I wanted to re-loggin now to my account so I've reached out to Poloniex Support to change the mail address so I can log in again. Indeed I was awaiting some sort of owner verification to assure I'm the owner of that account.
You have to secure your email and your account on Poloniex, passwords, 2FA, etc. It is abnormal if exchange allow you to change your email address.
It is suspicious change if you even can not log in your account and initial email.
Exchanges don't take risks and let customers change account information (initial email to new email) after access is lost like you.