I have to move email hosting from one server to another and are looking for the best practice for this procedure, in terms of continuity of email delivery with the least amount of changes at the email client level.
Currently, we are hosted on one server that all of the MX records are pointing to. Email clients are checking this mail server for new email and are leaving mail on the server for up to 10 days before deleting it. Most employees are also using iPhones and iPads to check email. All email clients are using POP and SMTP.
I know I can configure the new mail server, confirm it works, then switch the MX records, BUT the time it takes for the changes to get picked up all over the Internet means that some mail will continue to be delivered to the current server while some gets sent to the new server. The same applies to the email clients. Some clients will pickup the DNS change and start checking the new mail server (this assuming that I use the same mail server name and just update the IP), while other email clients will continue to check the old mail server for longer.
So what is the best practice to move to a new mail server, while allowing the email clients to get every last new email from the old mail server, then switch over without issue to checking the new mail server, all the while without having to visit and touch every client to setup a new mail account to check both servers during the transition?