I need some help to configure ISP Fail-over.
I have configured a Zimbra Mail Server on CentOS. It is working fine. We have 2 ISP connections and created 2 MX records for both ISP's like bellow
10.0.0.1 mail.example.com(mx) PTR record created in ISP1(Primary)
10.0.0.2 mail1.example.com(mx) PTR record created in ISP2(backup)
With this setup when my ISP1 is down we want to be able to access the Mail Server through ISP2. We are able to access mails internally.
But problem is users who are using mail services from outside organization have to change their mail client settings mail.example.com to mail1.example.com. They need to make the change to access their mail through through web access. They have to use mail1.example.com instead of mail.example.com
My requirement is we should not have to change any settings at user end, and when my ISP1 goes down it should automatically redirect to the MX record at ISP2
Can anybody suggest me how can I configure Fail-Over without changing any settings at mail client.
Best Answer
This has nothing to do with MX records. MX records are used for incoming mail over SMTP. What you are looking for is DNS failover for your mail.example.com DNS record.
Most decent DNS providers can provide this service. They will monitor the record (mail.example.com) and if it detects the IP is not reachable, will automatically switch the record to your secondary IP.
Obviously, there is going to be some delay as the DNS provider will need to detect the outage and the clients will need to pick up the updated IP. but, generally, the process works fairly well and usually fairly quickly.
edit:
MX records aren't PTR records either. Your MX records should point to the A records. The IP address used to send mail should have a corresponding PTR record.