IMAP Email Migration to Microsoft 365 from Rackspace, Zoho Mail, cPanel and GoDaddy Workspace Email: What IMAP Moves and What It Does Not

Microsoft's IMAP migration, run from the Exchange admin center or PowerShell, signs in to each source mailbox over IMAP, walks the folder tree and copies the messages into an Exchange Online mailbox that already exists. The folder structure is preserved. The source mailbox is read, not emptied, so the old system keeps working until you decide otherwise.

What it does not move, from Microsoft's own page on IMAP migration: contacts, calendar items and tasks. IMAP is a mail protocol, and Microsoft's tool never sees the host's contact and calendar stores. Add what lives in the mail client, which no server-side migration moves: Outlook rules, signatures, the autocomplete list, categories, and local folders or archives on the PC.

The limits, again from Microsoft: a maximum of 500,000 items per mailbox, and a maximum message size of 35 MB. Larger messages are skipped and reported; a mailbox over the item limit needs archiving at the source first. Folders such as Junk and Trash can be excluded from the batch.

So an IMAP migration is two workstreams: the mail, which the tool does, and everything else, which is a per-user checklist.

IMAP migration copies into a mailbox that must already exist and be licensed. That sets the order.

1. Tenant and domain. Create the tenant, add the domain, verify it with the TXT record. Do not change MX yet.
2. Users and licenses. Create the users with the same addresses as the source and assign licenses; a user with no Exchange Online license has no mailbox, and the batch has nowhere to write. At Microsoft list price, September 2026 price list, annual commitment, Exchange Online (Plan 1) is $48.00 per user per year ($4.00 per month) for mailbox only and Microsoft 365 Business Basic is $84.00 ($7.00 per month) with Teams, SharePoint and OneDrive. We sell both at Microsoft's list price.
3. Credentials. The batch signs in as each user, or as an administrator account the host allows to open every mailbox. Most hosts here have no such account, so you either collect each user's password or reset them all in a coordinated window; decide which before you promise a date.
4. The migration endpoint. Exchange Online needs the host name, the port (993 with SSL on every host here) and a test mailbox.
5. The CSV. One row per mailbox: the Exchange Online address, the source user name, the password.
6. Initial sync. Start the batch days before the cutover. The tool keeps syncing until you complete or stop the batch.

Each host's IMAP endpoint (confirm on the vendor's current settings page): Rackspace Email uses secure.emailsrvr.com; Zoho Mail uses imap.zoho.com for personal accounts and imappro.zoho.com for organization accounts on a custom domain, with IMAP access switched on per user in Zoho's settings; GoDaddy Workspace Email uses imap.secureserver.net; cPanel hosts use the server host name or mail.yourdomain, shown on cPanel's connect-a-device page.

Two limits set the pace. On the Microsoft side, migration-service throttling runs 20 mailboxes at a time across all batches by default, and the migration endpoint can be raised to a maximum of 100 concurrent migrations with Set-MigrationEndpoint. On the host side, every provider has per-user, per-IP and total connection limits, and a shared cPanel server will throttle or block a burst of connections. Microsoft's guidance is to have the host allow the maximum number of connections for the migration window.

The practical result: mail copies at the rate the host allows, not the rate Exchange Online could accept. A 10 GB mailbox on a throttled host can take a day. Start the initial sync a week before cutover and fix the skipped items and failed logins the batch report shows before the weekend. After the initial sync, the batch re-checks the source every 24 hours and copies new mail, so nothing sent during the week is lost.

The initial sync is the long part; the cutover is a sequence of DNS changes and one final sync.

1. Lower the TTL on the MX record a few days ahead.
2. Confirm the batch: every mailbox synced, item counts within reason of the source, no failed logins.
3. Publish Autodiscover for the domain pointing at Microsoft 365, and update SPF to include Microsoft's servers alongside the old host for the overlap. Do the DKIM and DMARC work in the order SPF, DKIM and DMARC for Microsoft 365 sets out, because a new mail system with no DKIM lands in spam folders on Monday.
4. Change MX to Microsoft 365. Mail that arrives at the old host during propagation is caught by the next synchronization.
5. Run a final sync, then complete the batch. Completing stops the incremental copies, so do it after propagation has finished.
6. Reconfigure clients. An IMAP profile in Outlook does not turn into an Exchange profile; each desktop gets a new profile, and each phone a new account.
7. Remove the old host from SPF once no mail leaves it, and keep the old mailboxes readable for 30 days.

If the move coincides with a new company name, do the domain work first. Changing Your Company Email Domain After a Rebrand sets out the order, since it is easier to migrate into the final addresses than to rename them later.

The second workstream. For each user, before cutover:

• Contacts and calendar: export from the host's webmail (most support CSV for contacts and ICS for calendars) or from Outlook, then import into the new mailbox.
• Local Outlook data: Personal Folders (PST) files that people created over the years to get around the host's quota. Our Exchange Online PST File Migration ingests them into the mailbox or the online archive at $45 per file plus a $1,900 tenant fee, which is the point to decide whether Exchange Online (Plan 2), at $96.00 per user per year at Microsoft list price on the September 2026 price list, is the right license for the heavy users.
• Rules, signatures and autocomplete are recreated by the user; a one-page guide the week before saves a day of tickets.

A word on GoDaddy. GoDaddy has said it is retiring Workspace Email and moving those accounts to Microsoft 365 purchased from GoDaddy, with users reconfiguring their clients afterward. That is a different destination from a tenant you own, billed and administered through GoDaddy. If you would rather hold your own tenant, migrate by IMAP before GoDaddy moves you, or, if it has already happened, GoDaddy Microsoft 365 Defederation explains the way out.

Our Cutover Exchange Online Migration from any IMAP Email System runs the tenant setup, endpoint, batch, MX cutover and completion in one week, and is Microsoft-sponsored for eligible customers, subject to Microsoft's eligibility rules; Microsoft-Funded Migration: What to Check Before You Buy sets out what Microsoft looks at. Where the scope goes beyond plain IMAP, or you want the contacts, calendars and client work done by us, Cutover Email Migration from Any Source System is $50 per mailbox plus a $2,500 tenant fee over seven days. The migration estimator prices both from a mailbox list.

Does IMAP migration move contacts and calendars?

No. Microsoft's IMAP migration copies mail folders only; contacts, calendar items and tasks are not migrated, and rules, signatures and autocomplete live in the client. Export and import those per user, or plan a PST pass.

How long does an IMAP migration to Office 365 take?

The initial copy runs at the pace the source host allows. Start it a week ahead; the cutover itself is a weekend of DNS changes, a final sync and client reconfiguration.

Do I change the MX record before or after the migration?

After the initial sync and before the final one. Change MX once every mailbox has synced, let the batch pick up the stragglers that arrived at the old host during propagation, then complete the batch.

Can I migrate cPanel email to Microsoft 365 without every user's password?

Usually not. cPanel has no administrator account that can open every mailbox over IMAP, so the batch needs each password. The workable pattern is a coordinated password reset.

What is the size limit for an IMAP migration?

500,000 items per mailbox and 35 MB per message, per Microsoft's documentation. Larger messages are skipped and listed in the batch report; larger mailboxes are trimmed at the source or split across a PST pass.

• Microsoft Learn, "What you need to know about migrating your IMAP mailboxes to Microsoft 365 or Office 365": mail folders only, 500,000 items per mailbox, 35 MB message size, mailboxes must exist first, synchronization every 24 hours until the batch is stopped or completed; Microsoft Learn migration performance guidance and "Tips for optimizing IMAP migrations in Exchange Online": 20 concurrent migrations by default, maximum of 100 per endpoint, host connection limits. Not opened from this environment; as reported by epcgroup.net and search excerpts on 27 September 2026; verify on Microsoft Learn.
• GoDaddy Help, "My Workspace Email is moving to Microsoft 365": Workspace Email retirement and the move to Microsoft 365 from GoDaddy; vendor IMAP settings pages for Rackspace Email, Zoho Mail and GoDaddy Workspace Email (host names and Zoho's per-user IMAP setting). Not opened from this environment; as reported by search excerpts on 27 September 2026; confirm on the vendor's current page.
• IT Partner blog articles linked above: GoDaddy defederation, domain change after a rebrand, SPF, DKIM and DMARC, funded migration eligibility
• IT Partner price sheet, Commercial segment, September 2026 US price list; IT Partner service pages and engineering notes, September 2026