Need an irule to block incoming connections if not matching a defined data group of addresses

Hello,

Edit - just realized I had [TCP::client_addr] instead of [IP:client_addr]

I'm relatively new as well, but you may want to try the below. If the traffic is going to port 25 and the client IP is not included in your allow list, it is set to drop the traffic. All others will go to the default pool, if one is set.

when CLIENT_ACCEPTED {
    Check if destination port is SMTP and the client IP is not in the allow list
    if {[[TCP::local_port] equals 25] and [class match [IP::client_addr] ne DATAGROUPNAME]}{
        Drop the traffic
        drop
}
}