Running a "DNS scan" to make sure my DNS zones are setup "correctly" led to the suggestion by the tool to run more than one mail server for redundancy. It got me thinking about how one would implement such thing.
Assume I have two mail servers, mx1.example.org and mx2.example.org. MX1 has higher priority. Assume each server is located geographically apart from each other. For any configuration related answers, assume they are running Postfix. How would I configure my MTA (Postfix) to consolidate email received by both mail servers into one response for clients?
Take the following example: I send an email to myself and it is delivered to mx1. Now mx1 has some downtime and someone sends me an email, it is delivered to mx2. My mail client is setup to use IMAP and retrieves mail from mx1. In the above scenario, I would only be able to retrieve the email I sent myself as the second email is sitting on mx2. In order for me to read the second email, mx1 needs to know about it from mx2.
Is this something I need to configure in my MDA, or does postfix have some feature to handle this situation?