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This tutorial describes how to mark a mail domain as a backup MX.
When smtp service on primary MX server is down, emails will be delivered to backup MX server. When backup MX server detects smtp service on primary MX is back online, it will relay received emails to primary MX.
To let other mail servers know your server is the backup MX server of this mail domain, you must add your mail server info in its MX type DNS record.
For example, main mail server of your mail domain
mx01.example.com, to set your iRedMail server
mx02.example.com as backup
example.com, you need to add
mx02.example.com as your lower priority
mail server in MX type DNS record.
example.com. 3600 IN MX 5 mx01.example.com example.com. 3600 IN MX 10 mx02.example.com
mx01.example.com has priority number
10. For mail service, the lowest number has highest priority.
so with above example, server
mx01.example.com is the primary MX, and
mx02.example.com is a backup MX.
When mail service on
mx01.example.com is down, other mail services will
It's easy to manage domain profile With iRedAdmin-Pro, including backup MX setting.
Go to domain profile page, click tab
Primary server address
It's recommended to set the IP address of primary MX as relay server to avoid mail loop.
SQL commands (we use MySQL for example):
USE vmail; UPDATE domain SET transport='relay:[18.104.22.168]:25',backupmx=1 WHERE domain='example.com';
In above example, we mark domain
example.com as a backup MX, and use IP
22.214.171.124 as primary MX server, you should replace it by the real
In domain object, please add LDAP attribute/value pair like below:
domainBackupMX: yes mtaTransport: relay:[126.96.36.199]:25