Inbound on port 25? I know my ISP does
Plus I just like having my data here, and not somewhere where I have no physical access.
This requires that your mail provider supports that port, of course, which is unfortunately not always the case.
They block port 25 to prevent open relays on their network (i.e. someone sends a forged email, the SMTP server does no authentication, and just forwards it on to the destination).