How smtp server record client source ip address

To get the client IP address, you have two choices : - Disable SNAT alltogether. The BigIP needs to be your email server default gateway. In this configuration, the BigIP simply routes back and forth the SMTP traffic, do what it has to do in the middle, but the SMTP server sees the client IP. - Make your email server support the PROXY protocol, and play around with iRules to make it work on the BigIP: Proxy Protocol : http://www.haproxy.org/download/1.5/doc/proxy-protocol.txt Example iRule for the BigIP side : https://devcentral.f5.com/s/articles/proxy-protocol-initiator Postfix for instance support the Proxy Protocol.