DA as fallback mailserver

[chow]

Hi, got the following scenario setup. Primary server is default server for the domains. It's not at our location and it's not running DA. On DA I created a MX record to forward all mail to this external server. How can I configure DA to be the fallback server. It should queue the mail when the default server is down and push the mail to this server when it's back up.

 

[nobaloney]

Hi, got the following scenario setup. Primary server is default server for the domains. It's not at our location and it's not running DA. On DA I created a MX record to forward all mail to this external server.

Are you forwarding mail from your server to what you call your primary server? That's a completely different scenario than if you're using MX records to tell the world to use the other server rather than your DA server.

How can I configure DA to be the fallback server. It should queue the mail when the default server is down and push the mail to this server when it's back up.

Are you keeping up to date mailbox lists on the DA server? If so then just creating forwards for each mailbox might work (not tested).

Otherwise you'll need to rewrite the exim.conf file to do what you want.

There's an article here explaining how the gnu.org domain runs an exim secondary nameserver.

Jeff

 

[MartijnHOS]

Hello,

Does somebody know how to setup a mailenvironment where two mailservers act as 1, with or without a kind of loadbalancer.

Is there a hardware solution or a good software solution to do this. For most of my clients mailfailures have got the highest priority so i want to know if there are some solutions i didn't think of.

If you copy the users and aliasses to a seconduary server i think the problem is that when the first is down the second whil take over but when the first is up again. Mail on the second server can't be downloaded by the user except when they added the ip as a second account in their mailprogram.


Kind regards,

Martijn

 

[chow]

@Martijn,

Normal setup would be primary mailserver on which the customer picks up his mail and a secondary mailserver which queues the mail when primary is down. When primary goes up again the secondary will empty the queue to the primary. This is a basic setup, nothing ordinary which works great. This setup was done easily with for example sendmail, took me less that 2 minutes to set this up. In DA I have severe problems getting this setup to work with exim.

 

[nobaloney]

Simple to do, but fraught with issues...

The main problem is, as Martijn writes, keeping the list of authorized recipients to use when the primary server goes down.

Sure it was easy to do with Sendmail. It's easy to do with Exim. As long as you don't care if you accept email for nonexistent (non-authorized) recipients if the main server is down.

I do care, because once I accept the email I'm responsible for either delivering it or returning it, and in today's world of spam and spoofed senders, that results in me having two choices on undelverable email:

I can throw it away, in which case I may have thrown away important email without notifying the sender, who thought it was delivered.

or

I can return it to whom I think is the sender, in which case I'm more often than not sending "collateral" spam, since the sender is most often spoofed.

Until now we've always believed there's no reasonable way to offer slave mail service on today's Internet, and many admins agree.

However, I've studied this a bit and I've reached the conclusion that we can offer the service under carefully controlled conditions...

We can offer it if we have software running on the master and sending us email information regularly so we'll always be up-to-date on the addresses for which we're supposed to be authoritative.

So we're looking at offering it with a plugin that will keep the slave server in sync with the master server, as far as authorized recipients is concerned.

We'll probably offer a slave service with a plugin in the near future; I have no idea how to price it.

And I know you'll still want to be able to do it yourself, especially if you have multiple mailservers in multiple data centers.

So go for it.

(We don't think it's easy to keep track of authorized recipients on a DA server using a relatively standard DA exim.conf file; we're going to use standalone servers.)

Jeff

 

[chow]

Since in practice the primary is only down for a short period the whole spam issue is a non issue I guess. Therefore a simple solution like the sendmail solution will do for the most of us.

 

[nobaloney]

The spam issue has been a major issue and this issue has been a major point of discussion on the professional lists for several years now.

I don't just make up my positions in a vacuum.

But if it works for you, fine.

Are you going to spam unsuspecting users by returning the mail you can't deliver? If so you'll find yourself on blocklists soon enough.

Are you going to just throw away undeliverable email? If so then you should probably notify your clients that you're making your email less robust than it was before you installed your secondary server.

Why do I believe this?

Because if you don't have a secondary server most mail servers (except for spammers) will attempt delivery for up to four days before giving up.

If you have a slave server that accepts email and then trashes it if it can't deliver it, the sending server will believe the mail was received properly. Even if it's thrown away.

It's the same as setting up a server wide catchall. On the mailserver hosting nobaloney.net, based on our rejectlogs, a slave server that didn't know which addresses weren't real could easily pick up thousands of undeliverable emails an hour.

So we don't think it's viable to act as a secondary server if we don't know which mailboxes are good.

Jeff