Migrate email from one server to another

As a web hosting provider, I would like the ability to migrate email independently of other data in WHM so that the migration process doesn't leave behind any emails that are received by the old server during the DNS changeover.

Whilst migrating cPanel servers its possible to transfer all data using WHM. It's also possible to do full backups for each account.

However, both of these processes are too bulky to be used multiple times in the migration process. During the migration, it's highly likely that numerous emails will be delivered to the old server whilst DNS propagates. There should be a migration script to grab these emails for all cpanel accounts as a reseller.

Telling customers to migrate manually shouldn't be needed, it shouldn't matter to them that a server migration is happening.

Migrating for them is far from easy. IMAP tools exist but require access to passwords which cPanel, rightly, doesn't offer.

The workaround solution for me was to use FTP to get a local copy of the old server mail directories and upload and new files to the new server. Once the local cache was built, such a script was quick enough to run several times during the migration process.

This seems totally unnecessary though. As a reseller I have access to every customer cpanel account and webmail account. There should be a very simple way in cPanel, or probably whm, to input the remote server and grab any missed emails.