[CentOS] Mail has quit working

> > 
> > > > Can you reach localhost by "normal" means?
> > > >      telnet localhost 25
> > > 
> > > I cannot.
> > 
> > 
> > Can you share the specific output of the command?  It might help. From
> > what you've told us, localhost resolves to the IPv6 local address, and
> > that address is present on your "lo" device.  You *should* be able to
> > connect.  The type of error might indicate what is still wrong with the
> > system.
> > 
> 
> Trying 71.28.79...
> telnet: connect to address 71.28.79.87: Connection timed out
> 

So are you saying that if you do 'telnet localhost 25' it actually
tries to connect to '71.28.79.87'?

If so, then that seems to indicate that host lookups are still being
done primarily through DNS and it isn't looking in your /etc/hosts
file.

What happens if you do 

  telnet 127.0.0.1 25

what about 

  telnet ::1 25

P.