Using a Specific SMTP instead of DNS for Internal Mail

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Using a Specific SMTP instead of DNS for Intern...
\ Peppe Top (14 Nov 2007)
. \ Michael Hallager (14 Nov 2007)
. . \ (Wietse Venema) (14 Nov 2007)
. . . \ Jason Ledford (14 Nov 2007)
. . . . \ mouss (14 Nov 2007)
. . . \ Peppe Top (14 Nov 2007)
. . . \ Peppe Top (14 Nov 2007)
. . . . \ Peppe Top (14 Nov 2007)
. . . . . \ Victor Duchovni (14 Nov 2007)
. . . . . . \ Peppe Top (14 Nov 2007)

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Subject:	Using a Specific SMTP instead of DNS for Internal Mail
Group:	Postfix-users
From:	Peppe Top
Date:	14 Nov 2007

Hi all,

I'm new to postfix and mail servers in general.
I'm doing my best to educate myself with the
available documentation but there is a lot of
material and if you could help me here, even
just pointing me in the right direction it would
be a big help.

I'm running two red hat enterprise linux 4 boxes.
One is on the inside (private address) and manages
the internal mail. The other has a public address
and manages the external mail. Both use postfix.

All users have internal account, something like
bob. Some have an external
account as well, like bob. All
the users access the mail with outlook via IMAP.

The "internal" outlook account is configured to
connect to the inside SMTP server. The "external"
outlook account is configured to connect to the
outside SMTP server.

Now when the big boys of my company (which
have both an "internal" and "external" account)
read the outside mail, from the public server,
sometimes they want to forward messages to
an "internal" address (bob).

All they should do is to forward email changing
identity in outlook, so that the client connects
to the inside server. (their PCs are already in our
private network, they don't do that from outside).
But they are annoyed by this, or sometimes forgot;
so they just want the mail to be sent without
changing identity.

The problem (at least for me) is that mail.domain.com
(outside postfix server) tries to send email to
mail.domain.inside and fails because it looks
for an MX record on the DNS, but the DNS knows
nothing about domain.inside, because its my
ISP DNS.

I tried to put mail.domain.inside IP into the
/etc/hosts file of mail.domain.com, but I quickly
realized that the problem is not with the A record.
Now I can ping mail.domain.inside, and even
connect to hi SMTP port from mail.domain.com.

So I think I need to inform Postfix that it
should not query the DNS for addresses like
*@domain.inside; it should instead connect
directly to mail.domain.isnide:SMTP.

I have the feeling that the /etc/postfix/transport
file and maybe transformation rules play a
role in the above, but a hint or two from you
veterans would be appreciated.

Thanks in advance
-- Giuseppe