Postfix w/ virtual domains & relay to ISP

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

I set up my mail using the excellent Virtual Mailhosting System with Postfix Guide, along with the Mail Filtering Guide, available at the Gentoo Docs, although I did a few modifications on the Mail Filtering part.

Currently I have two domains set: in one of them I am responsible for the MX record, so everything is done locally on my postfix install. The second domain is the troublesome one. I am not responsible for the MX record for this domain, so I use fetchmail to check for emails regularly on my ISP's pop3 server and have them delivered to my virtual mailboxes on my local postfix install.

My problem is on sending mail for the 2nd domain (everything is fine for the 1st one). On all the clients of the 2nd domain, I am using the ISP's SMTP server directly, but I would like to have them use my local postfix install, then have postfix to relay them to the ISP's SMTP server.

Searching a bit, I found two ways of doing it:

1) change the entry for the domain on the mysql transport table: currently, the entry for the 2nd domain is listed as maildrop:. I am using maildrop to filter mail server side (mainly moving spam to appropriate folders).

2) use relayhost setting on main.cf: according to the comments on main.cf, this entry will only be used if there are no matching entries on the transport table, which is not the case.

A more "visible" version of what I want. Here's the current scenario:

1st domain:
Client -> Postfix -> Internet

2nd domain:
Client -> ISP SMTP Server -> Internet

And here's what I need to do:

1st domain (doesn't change anything):
Client -> Postfix -> Internet

2nd domain:
Client -> Postfix -> ISP SMTP Server -> Internet

I am very new to postfix (first install), so I really don't know what to do to accomplish what I need. If anyone have any ideas, I would be happy to hear them. Also, I don't want to post unecessary lengthy config files, so if any configuration options are needed to help, please ask.

Thanks!

badchien · Guru Joined: 16 Feb 2004 Posts: 415 Location: doghouse

I use postfix, and I've come across this in the documentation:
http://www.postfix.org/postconf.5.html#sender_dependent_relayhost_maps

This sounds like the feature you are looking for, but I've never used it, so I can't offer much help with it. Hopefully you can research it and figure it out.

Good luck.

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

Hi badchien,

Thanks for the suggestion, it does looks like what I need. However that feature is available only on postfix 2.3, which is still in experimental state and not yet on portage. I'll look into that in the future, if there are no other options.

badchien · Guru Joined: 16 Feb 2004 Posts: 415 Location: doghouse

I hadn't noticed that

Bad luck.

It looks like 2.3 has been in development for some time. Hopefully a release is near.

magic919 · Posted: Tue Mar 07, 2006 9:26 pm Post subject:

Set up a dedicated transport for the second domain and use the ISPs SMTP as the destination.

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

magic919 · Posted: Tue Mar 07, 2006 10:30 pm Post subject:

I was more thinking of you using the dedicated transport for the outgoing stuff. I'd not do it in such a way that you lose your maildrop LDA.

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

magic919 · Posted: Wed Mar 08, 2006 7:51 am Post subject:

No probs.

It comes down to where you want to do the work, really. On the server side the simplest thing to implement is another Postfix instance listening on a fresh port. You have one on 25 and one on 10025 now. This instance would relay mail on to the ISP. Clients would need to aim for this non-standard port. You'd define this in master.cf, but leave off the content_filter as it's outgoing. If you have the luxury of additional interfaces you could use the standard port 25 on another interface.

Another option is to using regex or PCRE filter to match against the outgoing email for that domain. This would be inserted in main.cf under smtpd_x_restrictions. It would match the address and the result would be smtp:smtp.myisp.com . This is 'filter actions in access tables'.

badchien · Guru Joined: 16 Feb 2004 Posts: 415 Location: doghouse

magic919 · Posted: Wed Mar 08, 2006 12:39 pm Post subject:

You could slim that down and just add the

badchien · Guru Joined: 16 Feb 2004 Posts: 415 Location: doghouse

Could you explain that futher please?

I stopped both instances of postfix, edited /etc/postfix/master.cf as you suggested, and then started the primary instance of postfix. Now the primary postfix instance is listening on both IPs and the secondary instance and its configuration is essentially unused.

How does this allow incoming mail on the .11 address to be relayed through a different relayhost than that received on the .10 address?

magic919 · Posted: Thu Mar 09, 2006 7:46 am Post subject:

Sure. You can set up options on a per-listening-instance basis. So if you wanted teh top one to do content filtering but not the bottom one you 'd make sure no content filter in main.cf and add

-o content_filter

to top one. You can set lots of options in this manner.

You can even override global options with

-o global_option =

and leave it blank.

Hope this makes sense.

badchien · Guru Joined: 16 Feb 2004 Posts: 415 Location: doghouse

Ok, I understand that. I'm not as concerned with content filter as the OP. I was curious specifically about relayhost. As far as I can tell you cannot set different relayhost options per listening IP in master.cf. I tried it-- it doesn't work. Are you saying this should somehow work or are we misunderstanding eachother?

magic919 · Posted: Thu Mar 09, 2006 12:16 pm Post subject:

Okay. Yes, I'm saying it should somehow work.

I'd opt for the easy route and drop in

-o smtpd_recipient_restrictions = check_recipient_access pcre:/etc/postfix/use_isp_smtp

with the content of

/etc/postfix/use_isp_smtp

/./ smtp:smtp.example.com

The PCRE matches on anything and so all mail goes to the next hop you insert in use_isp_smtp file.

There may well be another way to do this, of course. You could have defined it as the content_filter but that just seems plain nasty.

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

Sorry for the late reply. I chose the pcre way of doing it, like this:

In main.cf, I added smtpd_sender_restrictions = check_sender_access pcre:/etc/postfix/use_isp_smtp. The content of use_isp_smtp is /^From: .*@domain2.com/ smtp:smtp.isp.com. Now everything is as I asked, thanks a lot for your help!

However, I have one extra request. With the above solution, every email sent from and to *@domain2.com is unnecessarily relayed thru the isp smtp server, while it could be simply delivered locally. I tried using if conditions on the pcre tables, like this:

magic919 · Posted: Thu Mar 09, 2006 5:08 pm Post subject:

Generally I have an allow above for the 'local' stuff. permit_mynetworks is enough on most of mine. If this doesn't work for you then stack the PCREs.

gmichels · Guru Joined: 20 Jun 2003 Posts: 480 Location: Brazil

Hi

First I'd like to thank you for your patience, I am learning a lot from this topic.

To be honest, I didn't understand what you meant on your last post, but I thought of another solution for my situation, which would combine the two suggestions you made previously. I was thinking of creating that outgoing-only postfix instance, then use pcre on the To: field to change the transport method. As everyone on the From: field for this postfix instance would be from my domain, this check on the To: field would be enough.

However I am having troubles trying to make this outgoing-only postfix instance relay mail to the ISP smtp server. Maybe it will be easier if I post my setup: