ok..if my live IP for mail server is 202.188.138.178 , so i shouls set this IP for Relay mail for
No.
Assuming you have the full class C:
"relay for addreses" = 202.188.138.0 netmask: 255.255.255.0
(Faizal: I just tried to see your ip address block and rDNS at SamSpade.org but 202.188.138.178 is not even findable according to Asia-Pacific nic's nameserver ns.apnic.net.
Warning: if your reverse ip, the PTR record, is not defined for you Imail server, many, and increasingly numerous, mailservers will not accept mail from you. Contact your upstream provider to help you setup your reverse zone and PTR records AT LEAST for your Imail machine.)
The above is how you "trust" ip addreses, ie, my_networks, and allow your Imail to relay all mail (ie, Imail will always accept and deliver "MAIL FROM: anywhere" to "RCPT TO: @anywhere-but-Chez-Faizal") as long as the mail is sent from an ip in your "relay for addresses" field.
Len
