Where I work we are having some problems with sending bulk email from a single public IP address, as several emails are being blocked or delayed.
Currently the server has a 1-to-1 NAT with a specific .73 IP address.
The request I got is to distribute email sending to 2 different public Ip addresses, and I immediately thought of using a NAT with PAT pool in round robin.
I then used this configuration on my Cisco ASA-SM to try to distribute the outbound SMTP "load" over the 2 IP addresses, namely .73 and .74, keeping the .73 for access to other services on the Internet:
nat (webdmz,outside) source dynamic email-server pat-pool smtp_addresses_range round-robin service smtp smtp description For SMTP email send
-
object-group network smtp_addresses_range
description Used in Round-robin for email send
network-object host xx.yy.zz.73
network-object host xx.yy.zz.74
-
# THIS IS THE ORIGINAL 1-to-1 NAT THAT MUST BE KEPT
object network email-server
host 10.aa.bb.73
nat (webdmz,outside) static xx.yy.zz.73
The problem is that all the connections were always NAT'ed using the .73 address.
