What copies across, what does not, and the one moment in a migration where mail can go astray.
Resources / Can I move to Microsoft 365 without losing my email?
Yes. A migration copies your email into Microsoft 365; it does not delete anything from your old system, and new mail keeps arriving at the old mailbox until the moment you switch over. The two things to get right are what comes across from where you are now, because from a typical web host's mailbox only the email moves, not calendars or contacts,1 and the switch itself, which is the only point in the process where mail can go astray.
Your old mailbox stays intact during the move
What moves from a typical web host's mailbox
The one moment that needs care
Not if it is done properly. Microsoft's migration tools copy items from your old mailbox into the new one, and your old system keeps working the whole time, so your team carries on as normal until the switch. Nothing is removed from the old mailbox by the migration itself.
There are limits, but they rarely bite a small business. From a standard email host, Microsoft migrates up to 500,000 items per mailbox, newest first, and the largest single email it will move is 35 MB.2 If someone has years of mail with very large attachments, that is worth checking before you start rather than after.
Keep the old mailboxes running until everything is confirmed in the new ones. Cancelling the old email service the day after the switch is a common way people genuinely lose mail.
From a web host's email, the kind that comes with many hosting plans and cPanel accounts, Microsoft uses what it calls an IMAP migration. That moves the mail in the inbox and other folders, and nothing else. Contacts, calendars and tasks have to be moved separately.1 It is not hard, but it has to be on the list, or the first sign is an empty calendar on Monday.
From Google Workspace, Microsoft's own tool moves mail and mail rules, calendars and contacts. Shared calendars and event colours do not come across, and moved rules arrive switched off, so someone has to check and turn them back on.3
From an older Exchange server, a cutover migration moves email, calendars and contacts together.1 From a personal Gmail account, it is the IMAP route again: email only.
Make a list of every mailbox, and then the ones people forget: shared addresses such as info@ and accounts@, and aliases that deliver to someone's inbox. These need to exist in Microsoft 365 before the copy, and they are often where customers actually write to you.
Then list everything that sends email without a person: the website's contact form, the scanner or printer that emails scans, the invoicing or booking software. After the switch each of them needs to send through Microsoft 365, or be allowed to send for your domain, or their messages will quietly stop arriving or land in spam.
Finally, tidy up. Very large mailboxes take longer to copy, so emptying the deleted items and clearing out old newsletters before you start makes the whole move faster.
Your domain has a record, the MX record, that tells the world where to deliver your email. During the migration it still points at your old system, which is why nothing changes for your team while the copying happens. On switch day it is changed to point at Microsoft 365.
Two details make that day safe. First, lower the record's time-to-live to an hour or less before you start, so the change takes effect quickly. Second, keep the old system and the migration running afterwards, because other people's email systems can take up to 72 hours to notice the change. Microsoft is explicit that once the migration is removed, mail that still lands in the old system is no longer copied across.4
Done in that order, mail that arrives in the gap still ends up in the new mailbox. Done out of order, a few days of email can end up in a system nobody is checking.
Mostly, a new place to sign in. Outlook usually needs the account set up again, and for some migration types Microsoft says users must create a new Outlook profile.5 Phones and tablets generally need the email account removed and added again with the new details.
Their email, folders and, where they came across, calendars and contacts will be where they expect. What does not come across on its own are email signatures, and anything set up on one computer only, such as local archive files. Those are worth a quick check with each person.
Plan the switch for the end of a working week, give everyone a one-page note on what to do on the first morning, and have someone available to help. Most of the stress in a migration is people not knowing what to expect.
For a handful of mailboxes coming from a standard email host, yes, if you are comfortable with DNS records and follow Microsoft's guide carefully. The steps are well documented.
The things that trip people up are the ones above: forgetting that calendars and contacts do not move over IMAP, changing the MX record before the copy has caught up, cancelling the old service too early, and missing the other DNS records that make Outlook and phones connect automatically and keep your email out of spam folders.
Our Microsoft 365 migrations start from $1,200, and cover the planning, the copy, the switch and the first morning with your team. Our guide to how long a migration takes covers the timeline in more detail.
How long does a Microsoft 365 migration actually take?: The timeline, from first call to the morning after the switch.
Microsoft 365 migration plan for Sydney small businesses: The ten-step plan, what it costs, and what you need to have ready.
Does Microsoft back up my emails and files?: Once you are on Microsoft 365, the part most businesses assume is covered and is not.
Not if the migration is done properly. Microsoft's tools copy mail into the new mailboxes without deleting it from the old system, and new mail keeps arriving at the old mailbox until the switch. Keep the old service running until everything is confirmed.
It depends where you are moving from. From Google Workspace or an Exchange server, calendars and contacts move with the email. From a typical web host's mailbox, Microsoft's IMAP migration moves email only, so calendars and contacts need a separate step.
It keeps arriving at your old mailbox and is copied across, until your MX record is changed to point at Microsoft 365. Keep the migration and the old system running for a few days after the switch, since some senders take up to 72 hours to notice the change.
Usually, yes. Outlook generally needs the account set up again, and for some migration types Microsoft says users must create a new Outlook profile. Phones usually need the account removed and added again.
Our migrations start from $1,200 and cover planning, the mailbox copy, the switch and support on the first morning. The final price depends on the number of mailboxes, where you are moving from and how much data there is.
Tell us how many people you have and where your email lives now. We will tell you what comes across, what needs a separate step, and what the move would cost. Free 30-minute call.
Prefer to talk? Call (02) 9053 8789.
Belivanis Information Systems