Re: [CentOS] IMAP security

These, it seems, are outgoing packets. Why, then, have they got those source addresses? Is someone managing to bounce packets through my mail server to hide their tracks?

I've never seen many of these, just the occasional one. Sometimes they seem to relate to an ntp source. Often they seem to come from a university site. I think the fact that I don't see many means that I'm not being used as an open relay, but I'm not 100% confident of that. I'd like to understand what's happening.

open relay is not to so with IMAP - thats SMTP

if this is an issue rather than just forwarding the ports setup an openvpn server on your LAN machine access your LAN using the VPN.