What protocol does mail.ru use when working with other mailboxes?

Question

Communication protocols

Recently, the mail.ru service has another opportunity, namely, work with other mail systems yadi.sk/d/OUypdHBDFkAUw .
More details here e.mail.ru/promopage/vvp. What protocol does the service use for such control? And than it can be fraught?
After all, the mail.ru service, as you know, is "leaky".

Answer 1

In this case, the mail server acts as a mail client, periodically checking mail using the POP3 or IMAP protocol. Sending can occur either similarly to an email client, via SMTP, or directly with a different sender address.
Consequences - control over mail, possible "loss" of your password.
If letters are sent directly from the mail.ru server, then the probability of getting the letter into spam is higher. I don't know the probability, but I think that the points for spam are high.

Answer 2

Where did you get the idea that he is full of holes? This opinion is purely connected with holey users, over the years of using mail, not a single letter was stolen from me, which seems to me to be a very good indicator of reliability.
And that users are full of holes and lose passwords so it does not depend on the service.