On Tue, Nov 03, 2009 at 07:57:35PM +0000, Paul Tansom wrote:

** Chris G <cl@isbd.net> [2009-11-03 18:49]:

...

I am moving my mail server from my desktop machine to a server machine. Both these machines are on my SoHo LAN behind a NAT router. Thus to move incoming mail from one to the other I have to change the port forwarding and firewall setings in the router.

Can anyone suggest a way to either send incoming mail to both machines or some other way of testing the new mail server before committing all my incoming mail to it?

I already copy all my mail to another user where it isn't sorted but just gets kept for seven days and then deleted. That is done on my hosting companies system. So I have some protection from total disaster! In addition of course the 'sender' (my hosting supplier) will wait and retry if/when I stop accepting mail so mail shouldn't be lost but I'd really like to do at least some simple testing before the big switch over. ** end quote [Chris G]

There's not enough detail of the nature of the setup to make specific suggestions, but one way you could use it to forward another port to the new machine. Then you can either telnet into the new port to test things out in a small way [1], and/or configure another domain/sub-domain to send mail into the new server [2].

Yes, I can send mail to the new machine using a different port. The problem is how to transfer some mail traffic to the non-standard port.

Just a couple of ideas that sprung to mind. I have a selection of domains and full control of my external mail server configuration including a full shell (virtual server), so this is along the lines I'd look at. I'm in the process of doing this myself and will be doing something similar. For a while during the process I'll be routing mail through the old server and forwarding it on to the new one using hubbed_hosts (Exim 4), which may be something you could adapt as well - i.e. forward on a particular mail account perhaps.

I have shell access on my hosting server but it's not a virtual machine so I don't have root access. I so have fairly flexible control of the mail routing. That's how I am able to send mail to multiple addresses.

[1] This either requires that you can telnet out through your connection and back in to the external port, or access to a shell session on an external computer (say work, or a suitable hosting account).

I have two shell accounts 'out there' so that's not a problem. So, yes, I can telnet into a non-standard port and make sure the SMTP server is answering.

[2] This may be more than your setup can manage. It may not be possible to set a different port, or configure a sub-domain for mail, and you may not be wanting to purchase an extra domain for testing!

No problem with domains or anything, that's what I do already to send my personal mail to my machine (it's what the SMTP server I'm talking about does in the main). My hosting service hosts isbd.net and isbd.co.uk, I have set up my home machine as chris.isbd.net and the mail gets sent there. The issue/problem is the NAT forwarding, I can't see a way to handle two streams of incoming SMTP mail with one sent to port 25 and one sent to a non-standard port. E.g. there's SMTP messages arriving at the 'outside' of the NAT router and the port forwarding and firewall are set up to route them to my desktop machine's port 25. There's no way I can see to split off mail for, say, test.isbd.net to a different port from that sent to chris.isbd.net. -- Chris Green

On Wed, Nov 04, 2009 at 04:46:16PM +0000, Paul Tansom wrote:

...

The issue/problem is the NAT forwarding, I can't see a way to handle two streams of incoming SMTP mail with one sent to port 25 and one sent to a non-standard port. E.g. there's SMTP messages arriving at the 'outside' of the NAT router and the port forwarding and firewall are set up to route them to my desktop machine's port 25. There's no way I can see to split off mail for, say, test.isbd.net to a different port from that sent to chris.isbd.net. ** end quote [Chris G]

As you say, you won't be able to differentiate between mail domains to route them differently using a basic NAT router. What you can do is telnet in to the alternative port and run the SMTP conversation manually, something along the lines of:

[snip details, thanks]

Alternatively if you have a server doing the forwarding then you may have the ability to configure a different port when you configure the domain routing details. That will depend on your setup. I've not tried it, although I keep meaning to check whether the Exim 4 hubbed_host feature can manage it, preferably on a per domain basis.

The router doing NAT is a Draytek Vigor 2820N which can do lots of clever things, I'll have a dig around. I do actually have two ADSL connections which the 2820N load balances (it has an ethernet WAN port as well as an ADSL connection), I can send mail to the other router as it has its own 'outside' address (in fact I'm already doing this). I suppose I could simply disconnect the other router from the 2820's ethernet WAN port (it'll fail over to using just one WAN) and then port map mail on the other router to a different port. It's all a bit messy though! :-) It's all down to how much effort I want to put into checking it before I get daring and do the 'big switchover'. -- Chris Green

You could also use swaks to test the mail server.