How to move from IMAP email to Exchange without losing anything

Why businesses outgrow IMAP

IMAP is a protocol for reading email stored on a server, and for that one job it is fine. What it cannot do is everything around email that a business comes to depend on: shared calendars with free/busy lookups, a company-wide address book, delegate access for a PA, shared mailboxes with proper permissions, instant push to phones and remote wipe when one is lost.

Exchange does all of that natively, which is why the move is usually prompted by a calendar problem rather than an email problem. The good news is that IMAP to Exchange is one of the most predictable migrations there is — provided you account for what IMAP was never storing.

Step 1: Audit what you have

Before touching anything, write down:

• Every mailbox and alias, including the ones forwarded somewhere and the ones nobody admits to using.
• Mailbox sizes. A few people will have 20 GB of mail; they drive the timeline.
• Where calendars and contacts live. In Outlook with IMAP they are typically in a local data file on each PC. On phones they may be in iCloud or a Google account.
• Every device and application that sends mail as your domain: multifunction printers that scan to email, your website’s contact form, accounting software, a CRM, an alarm system.
• Your current DNS: MX, SPF, any DKIM and DMARC records, and who controls the DNS.

Step 2: Lower your DNS TTLs

A few days before the cutover, reduce the TTL on your MX record (and anything else you will change) to five minutes or so. When you switch mail over, the change then takes effect quickly rather than over a day, and if you ever needed to roll back you could do so just as quickly.

Step 3: Build the destination and copy historic mail

Create the Exchange mailboxes, aliases, shared mailboxes and distribution groups first. Then copy the existing mail server-to-server over IMAP while the old system keeps running. Nobody is interrupted, and the bulk of the data — often years of it — moves in the background.

Watch for folder naming. Different IMAP servers name their special folders differently (“Sent”, “Sent Messages”, “INBOX.Sent”); a good migration maps them onto Exchange’s Sent Items, Deleted Items and Junk Email rather than leaving duplicates.

Step 4: Cut over

1. Change the MX record to point at Exchange. New mail starts arriving there as soon as senders pick up the change.
2. Add the Autodiscover record so Outlook and phones find the new server automatically.
3. Update SPF to include the new platform, and set up DKIM and DMARC so your mail is trusted by recipients.
4. Run a final delta sync to catch anything that arrived at the old server during the switch.

Done in the evening, this is typically finished well before staff arrive the next morning.

Step 5: Outlook profiles, calendars and contacts

This is where most DIY migrations go wrong. Outlook cannot convert an IMAP account into an Exchange account — each user needs a new Outlook profile with the Exchange mailbox in it. Then:

• Import calendars and contacts from the old local data file into the new Exchange mailbox, so they are on the server, synchronised and shareable for the first time.
• Recreate signatures, which are stored per profile and do not carry over.
• Check rules and auto-replies, which in an IMAP setup often ran on the PC rather than the server.
• Leave the old data file in place for a few weeks, disconnected, as a safety net.

Step 6: Phones and everything else

• Phones: remove the old IMAP account and add an Exchange account. Calendar and contacts now sync properly, and you can wipe the mailbox remotely if a phone is lost.
• Scanners and applications that send email need new SMTP settings, and usually authenticated SMTP on the submission port. Test each one.
• Forwarders and aliases should be recreated on Exchange, or retired if no longer needed.

The pitfalls that actually lose people mail

• Cancelling the old service too soon. Keep it running for at least a couple of weeks after cutover; some senders cache DNS longer than they should.
• Forgetting local calendars. If they were never on the IMAP server, an IMAP copy will never find them.
• Missing a sending device. The scanner that silently stops sending invoices is a classic.
• Leaving SPF pointing only at the old provider, so your outbound mail starts landing in recipients’ junk folders.
• Very large or corrupt folders that time out during copying. Spot them in the audit and give them extra time.

Or let someone else do it

Every step above is part of the free migration that comes with a MyExchangeServer mailbox: we audit, plan in writing, pre-copy your mail, cut over out of hours, rebuild the Outlook profiles and stay on the phone the next morning. You can read how our migrations work, or simply ask for a plan.