[TriLUG] email / DNS question

[Jason]

> 
> At work, we have several machines that need to send email
> to sysadmins, employees or customers.  Recently, we are
> seeing some of these emails bounce because the sending
> machine name is not resolvable on the external internet.
thats normal
> 
> The gateway machine is called "ncgw.nc.tmio.net" and all
> of our other machines in the building are "xxxx.nc.tmio.net".
> 
> I am a little bit confused as to whether "nc.tmio.net" is a
> host name or a subdomain name.  We seem to be using it as
> both.
tmio.net is the main domain (check this with whois)

jason at monsterjam jason $  host nc.tmio.net
nc.tmio.net has address 65.15.232.187
jason at monsterjam jason $ 

so that nc is a host.
> 
> If I try to send mail from any of our machines, some recipients
> will get the mail and others will not, depending on whether or
> not their mail server checks for valid sender addresses.
> Ironically, our corporate email provider is one that rejects
> these emails.
right

> 
> I would like for the outgoing emails to keep their original
> machine names in their FROM addresses.  For example, I would
> like to get sysadmin emails from "root at mickey.nc.tmio.net",
> and not just from "root at nc.tmio.net".
this doesnt matter, you can set your outgoing domain name in your mail client software.. thats why we have such a problem with spam 
today, you can forge a FROM header to be any domain you want.

> 
> Is this a DNS issue?  Or is this something that I can configure
> in postfix on the sending machines?  Or is there a deeper
> problem?

this is a simple dns/config problem. sounds like you need to have the proper DNS entries for whatever external address your natting 
your postfix box to.
i.e. A,PTR,MX dns records for 
postfixbox.nc.tmio.net = your.external.ip.address


Jason