[TYPO3-english] Do not get messages from powermail

[itisme itisme]

Hello!

I am the new user of TYPO3. Actually web designer who created site and supported  is unavailable (I can't reach him anyhow), but I faced with the problem that I do not know how to solve.

Everything was warking for long time, but one week ago I noticed that I do not get messages from my site with the sender addresses X (at) mail.ru. Any other addresses (even fake) are processed fine but those I do not get in my mailbox (in spam also).
I am using plugin powermail.

What could be the reason of that? Could you, please, help to solve this problem.

Thanks!