Hello.
How would one set back up mail server?
I have some customers that can't live without their email.
So they ask me if I can have backup mail server.
Now I have 2 reseller’s accounts on different serves.
How can I set those 2 servers to backup each other?
I know I can crate 2 DNS zones and MX record for each of the servers. But when what happened if one server is down mail will get to the other server.
But then how will the client set his config? I mean if its config is to get mail from the first server then how will he switch to the other one?
Please point me to the right direction.
Thanks

You will need to setup your second MX1 server to accept email and to store it until it can deliver email to MX1 server.

i hope this helps u.

Originally posted by apollo
You will need to setup your second MX1 server to accept email and to store it until it can deliver email to MX1 server.

i hope this helps u.

That’s exactly what I am asking.
How can I make it (the backup mail server) to store it and then deliver it?
Let’s say I have account in 2 servers.
Host1.com and host2.com
I create primary zone on host1.com
Secondary zone on host2.com
I put MX record on the zone for mail.host1.com and another MX record for mail.host2.com.
Now how can I make it so mail.host2.com will accept and store email while mail.host1.com is down?
How do I configure mail.host2.com to store the mail for mail.host1.com and deliver it to mail1 when it is back?
Thanks in advance

Let's say you have 2 servers blue.server.com -> IP 1.1.1.1 and green.server.com -> IP 1.1.1.2

In the zone records of each domain put

MX in A 1.1.1.1 with priority 10 and then
MX in A 1.1.1.2 with priority 100 if you want blue as the primary mail server

Put priority 10 for MX in A 1.1.1.2 if you want greenas the primary mail server

The lower the MX value the first the priority of mail going there

what SMTP server you plan to use?

you can use MX records to specify a bunch of different machines that will accept inbound mail for a particular domain.

but if you want the customer to be able to pick up that incoming mail with POP3 or IMAP or whatever, you'd need to set up some sort of round-robin or failover DNS so that the mailserver address they use in their email client points to a machine that's working.

that may be somewhat complicated - you probably don't want to create two (or more) independent mail spools for a user, which leads to some sort of network-based storage for mail, with NFS or whatever. most people I've talked to say "don't do that", at least if you've got a choice - it's likely to introduce slowness and instability. (and, now, you're probably talking about yet another physical machine to administer, repair, pay for, etc, with its own opportunity to fail.)

If you just want the mail to sit quietly on the secondary MX host until the primary MX is available again, no special action on your part is required - qmail does this automatically, it's been a couple of years since I used sendmail but I don't remember that behavior needing a lot of configuration (it's the default and expected behavior, after all.) you just need to be sure that the backup/secondary MX host knows that it should accept - but not deliver - mail destined for the domains being backed up.