Secondary MX record?

Posted on 2006-04-16
Medium Priority
Last Modified: 2006-11-18
Hello all,

We have an onsite Exchange server that handles all or our mail. We have a single MX record in DNS that points to it. I want to have a backup mail server through our ISP in case something ever happens to our primary. Can i just create a secondary MX record with a lower priority for the backup mail server? How does that work....all email will still go to our primary mail server and when it becomes unavailable for whatever reason, all mail starts routing to the secondary mail server until the primary comes back online? Thanks in advance!
Question by:markataylor76
  • 2

Expert Comment

ID: 16466101
Not aas simple,
it's not automatic,

if your primary server is down (or reject the mail for antivirus reasons or antispam, or ...), the mail try to be delivered to the secondary MX.

you need to ask your ISP to do

Expert Comment

ID: 16466107

you need to ask your ISP to do this job (accepting your emails and relaying them when the primary server come back)

but most of them do this job without any problem.
LVL 12

Expert Comment

ID: 16466122
Any professional ISP can host a mail fall-back service for you. When your mail server is unreachable for X attempts, the remote mail hosts will deliver mail to the secondary MX instead of returning it as undeliverable.

How mail is delivered when your server is back up depends. Sometimes this is automatic (because the mail host tries to push mail after some delay) or you'll have to use ETRN to signal the secondary MX that you're back online.

So, ask your ISP if it offers mail fallback for your domain.

Note that fallback only applies when your server is unreachable; a rejection because of viruses, spam, incorrect addresses, etc. will not deliver mail to the fallback host and the message will be returned undeliverable.

Accepted Solution

llefebure earned 2000 total points
ID: 16466268
Note that a lot of the spam sent these days is sent to your backup MX record first, then it tries the primary record if it has to. They do this because the backup mail servers commonly don't have the same level of anti-spam filtering that the primary ones do. If you notice more spam than usual, you'll want to make sure your ISP, or who ever is hosting your backup mail server, has anti-spam filters similar to your primary server's filters.

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