Mail delivery failed: returning message to sender

[Mail Delivery System]

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  dev-ma at ferra.ru
    SMTP error from remote mail server after RCPT TO:<dev-ma at ferra.ru>:
    host ferra.com.price.ru [172.16.0.25]: 550 5.1.1 Mailbox <dev-ma at ferra.ru> does not exist