Move email into Microsoft 365 (IMAP migration)

Move existing email into Microsoft 365 (Exchange Online) from Host Dada Email or any other IMAP provider, without losing messages or having downtime. Microsoft's built-in IMAP migration copies every mailbox's folders and emails, keeps them in sync until you switch over, and then you point your domain's MX record at Microsoft 365.

• Applies to: Microsoft 365 Business Basic, Standard and Premium; moving from Host Dada Email or another IMAP host
• Time: about 1 hour of work, plus copying time (hours to a day) and up to 72 hours before final clean-up
• Difficulty: Advanced

What moves and what doesn't

Before you start

• Microsoft 365 admin access (Global or Exchange Administrator).
• The password for every mailbox you're moving. If you don't know them, reset them at the old host and tell users the email will move. On Host Dada Email, reset passwords under Email Accounts in the Host Dada Control Panel (see Change or reset an email password).
• The old host's IMAP server name and port. For Host Dada Email it's imap.hostdada.uk, port 993, SSL. For other providers, check their help pages or the settings in an email app that already works.
• Access to your domain's DNS, so you can change the MX, autodiscover and SPF records at the end. If your domain uses Host Dada nameservers, you can do this in the Host Dada Control Panel, or we can do it for you.
• Tell your users. Explain the date of the switch, that they'll sign in with a new Microsoft 365 password, and that they should note their signatures and rules.

Step 1: Add your domain and users to Microsoft 365

1. Add and verify your domain in the Microsoft 365 admin centre. Add the MS=ms... TXT verification record, but when the wizard offers to set up email records, skip the MX change for now. See Connect your domain to Microsoft 365.
2. Create a user for each mailbox with exactly the same email address it has today, and assign each a licence. See Add a user and assign a licence.
3. Create shared mailboxes for team addresses (such as info@ or accounts@) instead of licensed users, if nobody signs in to them directly. They can be migrated the same way. See Create a shared mailbox.
4. Lower the MX record's TTL (time to live) at your DNS provider to 3600 seconds (1 hour) or less. This makes the final switch take effect faster.

Step 2: Create the migration CSV file

Create a spreadsheet with exactly these three headings in row 1, with no spaces, then one row per mailbox, and save it as CSV:

• EmailAddress is the Microsoft 365 mailbox to copy into.
• UserName is the sign-in name at the old host. For Host Dada Email and most providers that's the full email address.
• Password is the mailbox's password at the old host, not the Microsoft 365 password.

Step 3: Create the migration endpoint

1. Open the Exchange admin centre at admin.exchange.microsoft.com and go to Migration.
2. Select Endpoints (top right), then Add endpoint.
3. Choose IMAP as the migration type.
4. Enter the details: a name such as HostDadaIMAP, IMAP server imap.hostdada.uk (or your old provider's server), port 993 and encryption SSL. Leave the other settings at their defaults.
5. Select Create. Microsoft 365 tests the connection. If it fails, double-check the server name and port.

Step 4: Create and start the migration batch

1. In Migration, select Add migration batch. Give it a name with no spaces (for example Batch1), choose Migrate to Exchange Online and select Next.
2. Select IMAP migration as the migration type, then Next, and confirm the prerequisites page.
3. Choose the endpoint you created in Step 3.
4. Import your CSV file on the Add user mailboxes page.
5. Exclude folders if you want (optional). For example, you might skip Junk or Trash using the migration filtering options.
6. Schedule the batch. Choose who gets the report email, and start the batch automatically. Select Save, then Done.

The batch status changes to Syncing and then Synced. Select the batch to see progress per mailbox. Large mailboxes can take several hours. After the first copy, Microsoft 365 checks the old mailboxes for new mail roughly once every 24 hours.

Step 5: Check the copied email

Sign in to Outlook on the web as one of the migrated users and check that folders and older messages are there. Ask a couple of users to check their own mail.

Step 6: Switch your email to Microsoft 365

1. Pick a quiet time, such as a Friday evening.
2. Update your DNS records. Replace the old provider's records with Microsoft 365's:
   • MX: remove the old MX record (for Host Dada Email, mx.stackmail.com) and add yourbusiness-co-uk.mail.protection.outlook.com with priority 0. Copy the exact value from your domain's DNS records page in the Microsoft 365 admin centre.
   • Autodiscover: change the autodiscover CNAME to autodiscover.outlook.com.
   • SPF: replace the old SPF record with v=spf1 include:spf.protection.outlook.com -all. Keep only one SPF record, and only include other services if they really send mail as your domain.
   Full details are in Microsoft 365 DNS records on Host Dada nameservers.
3. Set users up in Outlook. Remove the old IMAP account from each device and add the Microsoft 365 account instead. See Outlook for Windows, Outlook for Mac and iPhone and Android.
4. Move contacts and calendars. Export them from the old webmail or email app (usually as .vcf or .csv for contacts and .ics for calendars) and import them in Outlook. If users kept everything in classic Outlook, its import and export wizard can move a .pst file across.
5. Recreate the extras: signatures, rules, automatic replies, forwarders (as aliases or groups) and catch-all addresses.

Step 7: Finish up (after 72 hours)

1. Leave the batch running for at least 72 hours after the MX change, so any mail delivered to the old host while DNS was updating is picked up by the daily sync.
2. Check the old mailboxes have stopped receiving new mail.
3. Delete the batch. In Migration, select the batch and choose Delete. This stops syncing; the copied email stays in Microsoft 365.
4. Cancel the old service only once you're sure nothing is left on it. If you're leaving a Host Dada Email plan, keep it for a few weeks as a safety net and open a ticket when you're ready to cancel.

Troubleshooting

The endpoint test fails or the batch shows "connection" errors

Check the IMAP server name, port 993 and SSL. Some providers limit how many connections one account or IP address can open at once; if so, migrate fewer mailboxes per batch. A password containing unusual characters can also be misread in the CSV, so try a simpler temporary password.

"Authentication failed" for some mailboxes

The username or password in the CSV is wrong for those rows. Sign in to the old webmail with the same details to test (for Host Dada Email, webmail.hostdada.uk). Fix the CSV and create a new batch for just those mailboxes.

"Mailbox not found" or the batch can't find the Microsoft 365 user

The EmailAddress in the CSV doesn't match a licensed Microsoft 365 mailbox. Check the user exists, has a licence with Exchange, and that the address is spelled exactly as shown under Users → Active users.

Some emails were skipped

Items larger than 35 MB, or corrupt messages, are skipped and listed in the batch report. Download them from the old webmail and forward them or save them to OneDrive before you cancel the old service.

Moving from Gmail or Google Workspace?

Google needs extra preparation (IMAP turned on and app passwords or a service account). Follow Microsoft's dedicated guide: Migrate Google Workspace mailboxes to Microsoft 365.

Last reviewed: October 2026