Backup/Redundant Mail

[ReN]

I relise this topic has been touched on but i've yet to find a solution in the forums to suit my needs , hence this post.

i was wondering if the DA team would take a lookinto the the feature in EXIM that would allow a seconday server also running exim to "callback" to the primary server to send on emails should the primary server go down.

I do know the above has been discussed please bare with me

the secondary server running exim can also check via means of AN SMTP connection to check if the msg would bounce. There would obviously be increased load on the secondary server , but in essence this would be an ideal mail backup system as it would only send on mail to legit users on the primary system.

 

[jamin1317]

the secondary server running exim can also check via means of AN SMTP connection to check if the msg would bounce.

This would be done via mysql or ldap. And the database would need to be replicated to the secondary server so lookups wouldn't fail when primary server goes down.

Don't hold your breath. It would take a major rewrite. Your best bet right now would be to get a couple dedicated email servers, buy a commercial email solution that has this built in, scrap DA's email functionality, as in turn off exim and change the template in DA to launch the commercial solution.

Or keep exim running and make the high-availablity email a premium service with a special template just for those accounts.

Check out zimbra. It can do what you are looking for.

http://wiki.zimbra.com/index.php?ti...ample_of_a_Typical_Multi-Server_Configuration

 

[ReN]

from what i've read exim does it , via a simple SMTP connection once the primary server comes back up. It Checks the email for a bounce responce for example and if it get ones doesn't deliver the email for obvious reasons , if it doesn't get a bounce from the primary email server it assumes the email addy is could and forwards on the email.

This is the reason i'd like the DA team to check it out - i beleive it is a viable and from the looks very simple process to do.

 

[jamin1317]

Thats just a basic secondary MX server.

Add to your DNS MX 20 mx2.domain.com.

On your secondary server change exim.conf

domainlist relay_domains = lsearch;/etc/virtual/domains : localhost

to

domainlist relay_domains = lsearch;/etc/virtual/domains : lsearch;/etc/secondarymx : localhost

create file /etc/secondarymx on secondary server and populate with list of domains to spool mail for.

Problem with secondary MX is spammers will start to send email directly to it even when primary server is still online.

Also, not big deal as most mail servers will keep trying to deliver mail for a few days if your one and only email server is not accepting connections.

 

[ReN]

if you read my original post , the basic way you described is correct , thats not what i'm after - exim callback feature is what it is called , even if spammers do try to send email directly to the secodnary mx - because the account wont exist on the primary they will get dropped.

 

[nobaloney]

from what i've read exim does it , via a simple SMTP connection once the primary server comes back up. It Checks the email for a bounce responce for example and if it get ones doesn't deliver the email for obvious reasons , if it doesn't get a bounce from the primary email server it assumes the email addy is could and forwards on the email.

This is the reason i'd like the DA team to check it out - i beleive it is a viable and from the looks very simple process to do.

Okay, so let's walk through this...

Your backup MX server waits until the main server is back. Then it checks and finds out that the email address doesn't exist on the main server. It finds the address doesn't exist.

What does it do with the email? You don't want to throw it away; it could easily be good email, even important email, with a small misspelling. And the RFCs hold you responsible for the email once you've accepted it.

You can't refuse it; you've already accepted it. Sure, you can send it back to the sender address (or even the from address) in the email, but if you do, then you'll be sending it back to an innocent victim of a spoofed address, who never sent it in the first place. And within a few days you'll rightfully be considered a spammer and find your server in blocklists.

Better to not accept it in the first place, to let it just stay on the sending server's queue until your receiving server is back up.

even if spammers do try to send email directly to the secodnary mx - because the account wont exist on the primary they will get dropped.

You can't just drop an email once you've accepted it. Not if it's real email.

Okay, drop it anyway; it's okay with me, but you're on your own.

However, what's the real reason I haven't considered creating code for a backup MX server in the DirectAdmin SpamBlocker exim.conf configuration file?

Simple: DirectAdmin isn't a backup MX server; it's a webserver that also accepts email for domains hosted on it. If you want a backup MX server create one. No reason to have DirectAdmin installed on it. Use exim or any other MTA.

Jeff