Postfix integration with Exchange 2003

bitpail · 10-06-2006, 11:52 AM

Hello everyone,
I'm new to these forums, any help that you can provided will be very appreciated. Currently we use Exchange 2003 for all our email services. We find the license for Exchange very restrictive but it is still desired that we use it for certain people in the company. However we need to provide everyone with a basic email account, this is where Postfix comes in. I want to setup a linux box (FC5) as our main MTA. Some user's mailboxes will reside on the linux box while others will remain in Exchange 2003. What I would like is for the linux box to just forward any mail for the Exchange users to the Exchange server, I don't want to user the pop connector from Exchange to pull the mail off the linux box because its limited to checking only every 15 minutes. The idea is that the Exchange SMTP server will still listen for incoming emails internally with Postfix feeding it for the Exchange users. Is this configuration possible with Postfix? If so can someone give me some pointers as to how I would go about doing this? I'm really new to Postfix, I need a kick in the right direction.

ghight · 10-06-2006, 12:43 PM

Well, it is possible, but to have some on one machine and some on another and forward between the two based on the username could get nasty. I'm rather positive you'd do this through the "virtual" table. Local accounts will need to be put in the "virtual" table to tell Postfix that everything gets forwarded but these. This is from the postfix website:

Code:

1 /etc/postfix/main.cf:
2     virtual_alias_maps = hash:/etc/postfix/virtual
3 
4 /etc/postfix/virtual:
5     root     root@localhost

I guess you could alias anyone going to the Exchange server as well

bitpail · 10-10-2006, 11:32 AM

By forwarding everything else do you mean by using the transport_maps parameter? What I'd like to do is forward only the exchange users as you mentioned last, that way I'm not forwarding unnessarily. How would you forward only the exchange users?

WindowBreaker · 10-13-2006, 09:00 PM

The simple way to implement this is with the optional transport table, as mentioned by another user. The downside is that it's not self updating, and you will have to manually update this table when new users are added, or old users are deleted.

That said, here's how it basically works. You determine where the majority of mailboxes will live (linux or exchange), and set that as the default destination. Then use the tranport table to override the default for all other users.

SCENARIO 1:
Most mailboxes will reside on linux, and a smaller number of mailboxes will reside on Exchange.

Assumptions:
Domain name: question.com
Exchange IP: 192.168.1.66
Some users to forward to exchange: larry, moe, and curly.

/etc/postfix/main.cf:
mydomain = question.com
myorigin=$mydomain
mydestination = localhost localhost.$mydomain $myhostname $mydomain
transport_maps = /etc/postfix/transport

/etc/postfix/transport:
larry@question.com smtp:[192.168.1.66]
moe@question.com smtp:[192.168.1.66]
curly@question.com smtp:[192.168.1.66]

Then run:

Code:

postmap hash:/etc/postfix/tranport

and

Code:

postfix reload

SCENARIO 2:
Most mailboxes will reside on exchange, and a smaller number of mailboxes will reside on linux. You want to deliver Moe, Larry, and Curly locally.

/etc/postfix/main.cf:
mydomain = question.com
myorigin=$mydomain
mydestination = localhost localhost.$mydomain $myhostname
relay_domains = $mydomain
relay_transport = smtp:[192.168.1.66]
transport_maps = /etc/postfix/transport

/etc/postfix/transport:
larry@question.com local
moe@question.com local
curly@question.com local

Then run:

Code:

postmap hash:/etc/postfix/tranport

and

Code:

postfix reload

Either way, every time you change /etc/postfix/transport, remember to run:

Code:

postmap hash:/etc/postfix/tranport

and

Code:

postfix reload

Again, this has a simpler setup, with higher maintenance overhead.

The alternative is a more complicated setup, with simpler (or none) maintenance overhead. This involves compiling Postfix with ldap support, and looking up exchange users via ldap queries to your domain controller. Again, this is not a simple setup and I don't know how exactly I'd implement it, so it would take some digging ( and a lot of testing) to get it to work.

Cheers,

Pablo

bitpail · 10-16-2006, 10:32 AM

Wow, what a great response, thanks for your help this worked out nice. Since our office is small, I don't expect this to be too much maintainance.

Thanks again for your help!

bitpail · 10-17-2006, 04:38 PM

On a related note....
I'm using dovecot for POP and IMAP. I would like to set it up so that all POP and IMAP requests go through the Linux box (ports 110, 143), however for the Exchange users I would like dovecot to forward those requests to the Exchange server. Can this be done?

ghight · 10-17-2006, 05:02 PM

Wow I really misread your last post so I'm going to delete what I just wrote,...

Sorry