Hello Guyzssss,
I am not in bug bounty so much, But while using one of the yandex service, I found that there was no Rate Limit Deployed for login attempts on their IMAP Authentication.
Means user can perform multiple attempts on their IMAP Service, Which is responsible to access yandex mail on other accounts.Just like others.
Like gmail users can import yandex emails(Account) using IMAP Authentication.