Mail Server Design | Part-2 | Separate Incoming and Outgoing Server

In this scenario, we are designing our email environment with multiple server, dedicating servers to perform only specific function. Our Email operation divided with 2 primary tasks, receiving and sending. We receive email for the users and we send email to various destinations.We are separating these two primary task with 2 different servers.

Please See the Topology Below:


Why we design this way?

1. First of all, single server means a “central point of failure”, if the server goes down, all email operation will be down also.

2. Normally, if we don’t need to deal with high volume email, we use just one single email server for all the email operations, but if we have huge email to handle, to reduce email processing time for delivery, either it is for incoming or outgoing, it is better to separate the incoming and outgoing operation with dedicated severs.

3. Another main cause of the separation is Blacklisting Issue, if our single server got blacklisted, both operation will hamper, but if our outgoing server got blacklisted for say, our incoming operation will not hamper.

Server Preparation Plan:

a. Incoming mail Server:

1. To receive email  we must configure our DNS server first, here our incoming mail server “” is the only MX for our domain, so any mail sent for  will come to our incoming server.

2. To receive email we must listen on 25 port to communicate with other mail server. We have to install any MTA like postfix, sendmail, exim etc… on this server.

3. As we have only 2 server,our incoming mail server must be configured to store email also, local users will retrieve mail from this server, that’s why we have to install POP/Imap service too.

4. Our user will use webmail, so we have to install webmail software also at this server.

5. Before receiving any email, we can configure our incoming server to scan all emails. If we can scan email prior receiving, users will get less spam. Though it is not mandatory for mail server but required.

b.Outgoingmail Server:

1. our outgoing mail server is only for sending mail, no other function here. It will work as smtp only, or relay server for the users.

2. Server has to listen on 25 port to receive Local Users Email. so we must install MTA like postfix, exim, sendmail etc..  here. Before sending any mail to outside, server will check the authenticity of the user, either sender is permitted or authenticated person to send mail by using our server.

So, here we are using 2 server separately for distinct functions, we can also make more complex setup with 2 servers only, we will move forward to those step by step.

To get the clear Picture, how this design works, please watch the video.

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