X-Forwarded Rule for SMTP

I never got it working. On my system it just hangs smtp. This is the script I ended up with but I don't really have a dev background, Just correct syntax/spelling and adjusted for have route domains on my system

    when CLIENT_ACCEPTED {
    set caddr [getfield [IP::client_addr] % 1]
    log local0. "Client addr: $caddr"
    STREAM::expression {@^EHLO.*\r\n@@ @^HELO.*\r\n@@}
    STREAM::enable
}

when STREAM_MATCHED {
    set mstring [STREAM::match]
    log local0. "STREAM_MATCHED: string: $mstring"
    set replacement [string range $mstring 0 1]
    append replacement "LO $caddr\r\n"
    log local0. "STREAM_MATCHED: replacement string: $replacement"
    STREAM::replace "$mstring $replacement"
    event STREAM_MATCHED disable
}

The above did not work when sending actual mails it breaks the flow. I have now used this code: https://devcentral.f5.com/questions/irule-for-smtp-passing-client-ip-addr-to-backend-mail-servers and now everything seems to work fine in my lab setup. Have not been able to test in a bigger environment to see the possible impact.