Mail Server Design | Part-4 | Incoming Mail Load Balancing

In this scenario, we are going to see how to deploy multiple incoming mail server to balance the load of incoming emails, this scenario is very common to big enterprise and isp environment. Where hundreds of thousands email comes per hour or per day.  to reduce load, we need multiple incoming server to handle incoming email simultaneously.


Why This Design:

main purpose is to balance the incoming email evenly with all server, so that one single server doesn’t get exhausted by receiving and scanning and delivering emails to internal mail storage.

How this design works:

1. at the domains DNS of all the domains we intend to receive email for, must setup MX record pointed to these 3 servers with same priority value, for example our 3 mail servers IP’s are,,, and we want to receive email for the domain We have to setup this Domains DNS MX record this way:             IN           MX         10              IN           MX         10              IN           MX         10 

when we assign this way, DNS will deliver the server ip with Round Robin fashion, whenever any sender tries to find our mail server, it will ask to our DNS server, and our server will answer with all these 3 server in round robin fashion, later we will try to see this in practical.

2. all 3 incoming mail server must have MTA installed so that they can receive email on 25 port.

3. Incoming Servers Must be configured with Mail Transport Rule or Mail Routing to Mail Storage Server.

About Email Routing:

All incoming server must make a Routing Decision based on the recipients domain Name, Or recipient Email addresses. after receiving emails  incoming server has to deliver the email to the recipient server, this time there is different different routing decision has to make by all 3 server based on the business requirement. Here in the second Diagram, we can see all incoming server are delivering email based on the recipient domain to different server.

To Understand the Scenarios Clearly Please Watch The Video.

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