I have web servers behind the ASA5500 that use an SMTP server to send email traffic. I need some assistance in configuring the router so the the email messages are from the desired IP address. Currently, all smtp messages are sent using the routers public IP address. I have a inbound NAT entry to translate a public IP to a private one for reverse lookup. Whenever it tries to reverse lookup, it fails beause the originating address is mot the one coded in the A record for that address, eg mail.test.com A record = 222.333.444.555. The router address is different.
I am assuming that when a SMTP server sends an outgoing email, that it uses the first IP address configured on the server. In my case, I have an address of 192.168.1.50 as the first, but the server also has IP's 192.168.1.100-120, which are part of an NLM cluster (server farm). Not sure if the network load balancing stuff matters, but how do I tell which IP address the SMTP server will use send sending the outgoing message? Seems that that address must be coded in the NAT table.
I suspect that this is a simple NAT entry, but I have tried it and can't get it to work. Can someone provide be the cli syntax to add a nat rule for this?