Mail.ru is protected

Today, an employee who uses Mail.ru asked to send her an invitation to Gmail. The invitation sent, but very soon was unpleasantly surprised.

Delivery to the following recipient failed permanently:

*****@mail.ru

Technical details of permanent failure:
PERM_FAILURE: SMTP Error (state 16): 550 spam message discarded.
If you think that the system is mistaken,
please report details to abuse@corp.mail.ru
')
- Original message - (...)
I use Gmail and I think you might like it too. Here is an invitation to create an account.
(...)

Someone improves the service, and someone tries to escape. Let in such a primitive way.