hi, i'm a newbie here. I already setup 2 domain using ISPConfig, e.g. www.pristronic.com.my and www.e-markplus.com. The first domain www.pristronic.com.my doesn't have any problems and working. But the second domain have error when receiving email. If I sending email from email@example.com to firstname.lastname@example.org, it's fine. But when I want to reply or to send a new message from email@example.com to firstname.lastname@example.org, it has a problem: This is an automatically generated Delivery Status Notification Delivery to the following recipient failed permanently: email@example.com Technical details of permanent failure: PERM_FAILURE: SMTP Error (state 9): 553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1) But sending and receiving is working between www.pristronic.com.my and www.e-markplus.com. What is the solution for this? Thanks.