The image attached above is a reference for this discussion.
So I have a mail server hosted within the company corporate network. This server is hosting multiple mail domains using Hmail server mail server application running on a server @ 192.168.100.100 as shown above.
A records of the following domains are pointing to respective public static IP address as shown.
Port forward for SMPT and POP3 are configured on the 3 public IP addresses towards mail server inside.
Each of the ISP have provided additional public static IP address .2 and .3.
Note that mail.domain3.com has an A Record pointing to 20.20.20.3 that is additional static IP address on WAN2 interface.
Peplink cannot route the traffic based on the context inside the SMTP packet. You can consider to bind multiple IP addresses on the mail server itself. For example 192.168.100.100, 192.168.100.101, 192.168.100.102. And setup the mail server use specific IP for specific domain.
With NAT Mappings (both Inbound and Outbound Mappings)
192.168.100.100 <-> 10.10.10.1
192.168.100.101 <-> 20.20.20.3
192.168.100.102 <-> 30.30.30.1
Because, each domain will have its own private IP, and with proper Outbound Policy, you can route the mail traffic of different domain via different ISP
OK, assuming I have 3 different private IP addresses for each of the mail server, how can I make sure that incoming and especially outgoing is passing through the same public IP addresss? Especially also for the 20.20.20.3 that is only an additional public iP address.
hmmm… looks it could work. however I am thinking this will also expose .101 from internet right? Firewall inbound can be used here to allow only relevant traffic??? i will test this one.
What I mean Lai is that all inbound types of traffic that will hit 20.20.20.3 will be forwarded to private IP .101 right .101 and .3 are being NAT mapped.??? inbound policy will be over ridden and that all I can do to make sure that only TCP 25 and 110 are allowed to be forwarded to .101 is to implement inbound firewall???