[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.