It is possible your email has been blacklisted - or account has an action block while you got verification. That means action block needs to expire in order for you to get the verification codes on email. One of those are your solution
You need to create a password in the mail.ru account that allows external applications to access the verification code
Here is what the MP team sent me when I asked about it
On the mail.ru email account, please go to Settings > All Settings > All security settings > then under Login Methods, click on Passwords for external applications > click Add and enter mp as the name (you may be asked again for the account password after this step, please enter it) then it will show the generated app password after (1st image below). Copy that and paste it on the Email validation tab’s password field, then TEST IMAP/POP3 again and you should get an ‘email is valid’ message (2nd image below)