SMTP iApp Template - Early Release
Problem this snippet solves: INITIAL RELEASE
Minimum required BIG-IP version: 11.4.0.
Supported BIG-IP versions: 11.4.0-12.0
v1.0.0rc1
iApp template for configuring standard load balancing, moni...
Published Apr 30, 2015
Version 1.0
Your other option is to use nPath: https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm_implementations_guide_10_1/sol_npath.html
TMK, for non-HTTP traffic, those are the only ways to get the real source IP.