EnterraHost
Rackspace runs more than one mail product, and which one you are on decides the whole approach. Standard email is an ordinary IMAP job. Hosted Exchange is not, and the difference is not a detail you can work out as you go.
Work out which product you have first
Rackspace Email is a standard mailbox read over IMAP or POP, and it copies the same way any other provider does. Rackspace Email Plus is the same mailbox with device synchronisation added, so the mail copies identically and what changes is which of our tiers is the closer match afterwards.
Hosted Exchange is Exchange underneath rather than plain IMAP. It does not copy over IMAP at all, and it moves from an exported file in the same way Microsoft 365 does. If you are on Hosted Exchange, read moving your mail from Microsoft 365 instead of the section below, because the sequence is the same and the order is reversed compared with an IMAP move.
For Rackspace Email and Email Plus
Two things are needed per mailbox. The IMAP server address, which is in the Rackspace control panel, and working credentials.
Do not collect customers' real passwords. Set a temporary password on each mailbox with Rackspace for the migration window, and tell people what it is. They can keep using their normal password to read their mail in the meantime if you set it up that way, and the migration has what it needs. The alternative is asking a customer for the password to their own mailbox, which nobody should be doing.
One warning that costs a whole batch if it is missed. If somebody changes their password after you have set the temporary one, that mailbox fails and has to be picked up in a retry. Small batches are what make a retry cheap, and moving your existing mail across covers the sequence around it.
Which tier matches your Rackspace plan
Standard Rackspace Email lines up with Lite, because both cover webmail, aliases, forwards, distribution lists and filtering.
Email Plus lines up with Pro, because the synchronisation it adds to phones and desktop clients is what Pro adds here.
Hosted Exchange is the awkward one, and it is worth being straight about it. Its closest equivalent here would have been a tier built for native Outlook connectivity, and that option has been withdrawn. What remains is Pro, which reaches Outlook calendar and contacts through the standard protocols rather than natively. That is a real difference from Hosted Exchange and worth testing on one mailbox before committing a whole organization to it.
The DNS change
Where you change the records depends on who manages the domain. If the domain is registered with us, your DNS lives in the toolbox and you edit the records there. If it is still with another registrar or DNS provider, the change happens in that provider's own panel, and you can either make it there or transfer the domain to us first and manage everything in one place afterwards.