I'm planning to get a new server soon, and I'm planning on moving half of my customers to the new server once it's set up. I've been thinking of how best to handle the transfer to make it as smooth as possible, and clearly setting up DNS clustering with a short TTL is the way to go. When it comes to mail delivery it would obviously be bad if messages were delivered to the old server after accounts were moved. To get around this, I'm thinking I'll temporarily configure exim to queue messages rather than delivering them. Messages will be kept in the queue until the transfers are complete, at which time the MX records for the domains will have been updated. Am I right in thinking that exim will then simply relay the messages to the new server?