I'm currently running droplet with Ubuntu 12.04 running postfix / dovecot mail server with virtual routing managed through Vimbadmin. I'm looking to migrate to a bigger droplet, both for the increased hardware supported and in order to update ubuntu to 14.04 along with several other packages which have caused problems when trying to update on the existing droplet, resulting in a loss of emails.

Is there a way to 'cache' or store any emails sent to the current mail server during the transition over to the new server which can then be sent on/retrieved once the new droplet is all setup and has the current DNS record set to the new IP etc?