Нужна консультация по mail сервису

Нужна консультация, как справиться с подобной вещью

:

xxx.xxx.xx.xx does not like recipient.

Remote host said: 550 5.7.1 ... Connect denied. IP name lookup failed for yyy.yyy.y.yyy

Giving up on xxx.xx.xx.xx.

:

vvv.vv.vvv.vvv does not like recipient.

Remote host said: 450 4.7.1 Client host rejected: cannot find your hostname, [yyy.yy.y.yyy]

Giving up on vvv.vv.vvv.vvv.

I'm not going to try again; this message has been in the queue too long.