Postfix mailgateway question
 

Hi all,

I am planning to build a mailgateway which has to do multiple routing.
This is the setup:

Path A.
Postfix Mailgateway is in DMZ.
MailGateway receives mail from the Internet, does some checks on AV and SPAM, then routes email to internal (Postfix) smtp-server.
The internal smtp-server distributes email to Exchange servers in several internal domains, say example.com
On the internal-smtp-server are mailboxes for "other" domains and users, to be reached by POP and IMAP (say this is for a.com, b.com and c.com). This is handled by Virtual_Domains etc.
On the Postfix MailGateway I 'm using "transport maps" to get all the mail for example.com, a.com, b.com and c.com routed to the internal smtp-server.
So far I'm cool. (I think. :-)

Path B.
The DMZ MailGateway is also planned for "mailwashing" the email for other maildomains that reside elsewhere on the Internet, say x.com y.com and z.com
For these domains the MX records in DNS point to our MailGateway, so the mail arrives, is then being washed and after that gets send over to the smtp-servers of x.com, y.com and z.com.

I have no experience how to configure this, since "transport maps" only apply for domains you host yourself.

So what type of route setting do I have to use here: will relay_domains do the job?
If so, will "relay_domains" combine with "transport maps"?

I hope to hear some real world advise.
Thanks!

Why wouldn't you use relay_domains and relay_transport?

Entries would be something like:

x.com smtp:mail.x.com
y.com smtp:mail.y.com
z.com smtp:mail.z.com


One thing you will want to consider is how you deal with nonexistent users though.

Hi billymayday, thanks for y'r answer.
I will take your suggestions into testing.
Nonexistent users are indeed an issue in this setup.

There's the relay_recipient_maps that should help.

See man 5 postconf

Hi billymayday,

I have been looking into this: by using relay_recipient_maps you have to know who exactly you users are.
So at he MailGateway-server, in the DMZ, I have to maintain some database(s) filled with valid users.
Isn't that typically a configuration item that is best handled by the smtp-servers at x.com, y.com and z.com?

C.

Sure is, but you'll be accepting the mail as relay, so either the relay checks or accepts all mail.

Hm..... yes, I realize that now.
Thanks for y'r feedback!

C