Author: Tim Jackson Date: To: exim-users Subject: Re: [exim] Virtual/Reseller Exim SMTP with dedicated IP/hostname
Paul Rupp wrote:
> I have just set up a shared hosting account on a commercial webserver
> with access to Exim. I sprung for a dedicated IP,
Dedicated IP for what? Web hosting?
> and the system administrator sets reverse DNS for me. I noticed, of course, given the standard configuration for Exim, that when I send
messages through "my" > smtp server, it picks up the IP of the shared host, and the hostname of
> the main system, and these are inserted into e-mail headers.
That's normal, unless you are paying the sysadmin to run a separate
instance of Exim just for you, which isn't common: if it matters that
much then people are normally getting virtual dedicated servers (based
on UML, Xen, linux-vserver etc.) If only a single instance is running,
then it's not "your" SMTP server at all, it's your provider's.
> What changes do we need to make to the configuration of Exim so that
> whenever a client/shared domain sends mail through Exim, Exim picks up
> the IP and hostname of the hosted domain rather than the default shared
> IP and system hostname?
This doesn't really make a lot of sense. In what sense is Exim "picking
up" an IP? In the sense of the "received from" host in headers,
"received by" host in headers, or do you mean the interface that it
sends *out* on? (and which is therefore "picked up" by other hosts?) All
three of those are instances where the "primary hostname" might appear.
> It seems like shared hosts with dedicated IP's everywhere would be
> asking how to do this- especially resellers.
Not really. Very few end users even know what an e-mail header is let
alone how to interpret it. It's just technical mumbo-jumbo to most. The
customers of resellers are thus highly unlikely to care (and not
unreasonably so, since there's no *technical* reason to obfuscate the
true source of the mail, and if people are that bothered about finding
out the business relationships, they can always go and look up the IP in
rwhois anyway). Therefore as I mentioned earlier, if it's *that*
important to someone that they must be seen as having exclusively "their
own" hostname when outgoing mails are sent, dedicated or virtual
dedicated servers are increasingly common, especially since they're so
cheap these days due to competition as even the larger providers get in
on the act.
A "dedicated IP" on a shared server is really only that: just another
interface on a shared server. If you want a complete "virtual
environment" where *everything* seems to be running on a different host
(and remember it's not just SMTP here: what happens if you go to the IP
address via HTTP, without a virtual host defined? What about
POP3/IMAP/other services, if they are also being provided on that
host?), then rather than trying to "fake" it, it's much easier just to
actually *really* run everything on a different host: that's when a
virtual server is definitely the way to go. (There are other advantages
too, like improved security)
