Secondary (backup) Email Server, How-to?

[ciuly]

Hello,

I am thinking to set up another dedicated server in some other town as a backup server for some of the services I host on my main server (web and email most importantly).

The problem I am having is with the email server.
What I want is that while my primary email server is offline for whatever reason, a secondary email will receive the emails (which is piece of cake correctly using MX records) AND the primary email server will get synched when it's back online.

Is there any way to pull this off with XMail? I haven't started anyhting yet, so I'm open to suggestions.

thanks.

[Sob]

The easiest solution is to configure custom domain on secondary server and relay all received messages to primary. It works, except there's a problem with bounce messages generated by the secondary server, when it accepts mail for all accounts and not only existing ones and primary server then refuses to accept it.

Some reading about it here:

http://xmailforum.homelinux.net/index.php?showtopic=3834

Includes my sample script for user synchronization. It's ment to be as simple as possible, so for serious use you probably want something better.

[YorYor]

Check this HOWTO out - even simpler solution using postfix to act as the backup mailbag.
http://www.howtoforge.com/postfix_backup_mx

Also, some simple anti-spam measures for the backup mx.
http://www.cyberciti.biz/tips/postfix-spam...ists-howto.html

The only thing you need to figure out is how to synchronise the "relay domains" parameter against your mail xmail server.

[ciuly]

thanks.

I have come up with a "better" idea for my setup. (not tested yet, since I have to first get the physical backup machine in it's place which is about 350 km from here but will happen in the next 1-2 months (it will backup most of my services).)
back to the idea:
- I will set up an almost exact xmail setup as on my primary machine
- there will be a service running on the primary looking out for modified configuration files, upon finding, it will rsync them to the secondary machine
- on the secondary machine there will be another service looking out for when the primary comes online, and when it does, it will rsync the email folders

the main thing is that I will keep other (backed up) services in sync as well using this idea.
if it'll work, I'll post back

[ciuly]

while searching for some more info on how to accomplish my task, I found this thread which is pretty interesting: http://xmailforum.homelinux.net/index.php?showtopic=3748
anyway, for some reason my 2.4.36.2 kernel is missing dnotify and I couldn't find anything which would seem the right package. I took a look at fam, but it appears that if it doesn't have imon pseudo driver installed in the kernel it will not behave optimally, instead it will poll the filesystem which is kind of stupid. I couldn't find a way to check if imon is loaded or at least presetn on my machine (couldn't find anything *imon* on the filesystem) so I dropped fam as well.


so I now reconsidered the scenario.
- my backup machine willa ctually be used when my primary machines goes down for whatever reason.
- my primary machine goes down in say at most 5% of the time. My ISP gives me 98% uptime but I also have quite a few power outages where I am. so 5% is a good figure
- when my primary machine goes down, it will do so for a few minutes (usually) about 30-60 minutes (rarely) and over a few hours maybe 3-5 times a year.
- I don't make changes ot the email config too often. actually, I do them ratehr rarely.
- the purpose of the backup machine is that when the primary goes down it will provide the same service (full email in this case and read-only http). basically, in case of email, it assures me that I do not loose emails (which shouldn't happen anyway since the sending smtp server should keep retrying for more than 6 hours but one never knows).
- I figure that running rsync every 60 minutes will ensure that I get all the emails from the backup machine in due time

for my setup this looks like an easy, fast and acceptable solution.