Problems with sendin PM's

[Hammerman]

Every time I try to send a privat message (after the recent host change), I get this error message:

Mail Error!

SMTP protocol failure!
Host: mail.lurkerlounge.com
Return Code: 553
Return Msg: 553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)
Invision Power Board Error:
Check your SMTP settings from the admin control panel

Any ideas on how to fix this?