iRule for SMTP: Passing Client IP Addr to backend mail servers

Thanks so much, John! Here's a new version of it based on your advice:

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

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

when SERVER_CONNECTED {
    STREAM::disable
}

I can't test this (it compiled alright) yet because my devices are all firewall'ed off at the moment.