Email Migration to Microsoft 365
Mailboxes moved into Exchange Online from webmail, on-premise Exchange, Google Workspace, Zoho Mail or years of PST files — with the method chosen for your source, not for our convenience.
This page is specifically about mail. For files, SharePoint structure and the full project, see Microsoft 365 migration.
The method depends on where you are coming from. On-premise Exchange below about fifty users is normally a cutover migration; larger estates move in batches through a minimal hybrid; anything coexisting for months, or keeping Exchange long-term, goes full hybrid. Microsoft’s own “staged migration”, which older guides still recommend, only supports Exchange 2003 and 2007 (checked 25 September 2026). cPanel webmail and Zoho Mail migrate over IMAP, which carries mail but not calendars or contacts. PST archives import separately. In every case, data is copied and verified while the old system stays live, and MX records change only afterwards.
Which migration path fits your source
These are not interchangeable, and the choice is made by what you are leaving rather than by preference.
Cutover migration
On-premise Exchange, smaller organisations
All mailboxes move in one pass and everyone switches together. Simple, predictable, and the right answer for most businesses below roughly fifty users. The trade-off is that everyone changes on the same day.
Minimal hybrid
Exchange 2010 and later, too large for one pass
A lightweight connection between the two sides, set up only so mailboxes can move in batches over days or weeks, then removed along with the server. Accounts stay synchronised throughout; calendar availability across the two sides does not, so each batch should be a team that works together.
Full hybrid
Months of coexistence, or Exchange staying on-premise
A persistent link between on-premise Exchange and Exchange Online with a shared address book and calendar availability across both. Genuinely powerful and genuinely involved — worth it where the two must run side by side for months, or where the on-premise server is staying for good reasons.
IMAP migration
cPanel webmail, Zoho Mail, most hosted mail
Mail is pulled mailbox by mailbox over IMAP. Reliable for messages and folders. Calendars and contacts are not carried by IMAP at all and are handled separately.
PST import
Archived mail on individual laptops
Historical mail sitting in PST files is imported into Exchange Online or into users' archive mailboxes. Usually the slowest part of any project, because the files are never where anyone thinks.
Third-party tooling
Google Workspace, complex or very large moves
Where the native paths do not cover the source well — Google Drive alongside Gmail, for instance — a dedicated migration tool carries more and reports better. Licensed per project and included in the quote.
What an IMAP migration does and does not carry
IMAP is the most common path out of shared hosting and hosted mail, and it is also the one most often quoted without its limitations attached. Two of these rows are why people are unhappy in week one.
| Item | Carried by IMAP | Notes |
|---|---|---|
| Email messages and folders | Yes | Including nested folders and read/unread state |
| Calendars | No | IMAP does not carry calendar data — exported and imported separately |
| Contacts | No | Exported from the source and imported separately |
| Server-side rules | No | Rebuilt in Outlook after the move; complex ones need redoing by hand |
| Shared and role mailboxes | Yes | Migrated, then recreated as unlicensed shared mailboxes on the new side |
| Mail sent during the move | Delta sync | A second pass after cutover catches anything that arrived mid-transition |
Four things that decide how long it takes
Notice that user count is not on this list. A migration is paced by data volume and by how fast the source will let go of it.
Total data volume
The single biggest driver of elapsed time. Twenty mailboxes averaging 2 GB is a different project from twenty averaging 40 GB, and the second one needs staging well before the cutover weekend.
Source throttling
Most source systems rate-limit how fast mail can be pulled, and shared hosting is often the worst. This — not your internet connection — usually sets the pace, and it is why a migration is planned in days rather than hours.
DNS TTL
Lowered several days before cutover so the MX change propagates in under an hour instead of over a day. Skipping this is the most common cause of a rough switchover.
Number of devices per person
Every phone, tablet and laptop needs its account reconfigured. Twelve people is fine; twelve people discovering it unprompted on Monday morning is not.
Email migration — common questions
helpHow long does email migration to Microsoft 365 take?
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Elapsed time is driven by total mailbox volume and how aggressively the source system throttles, not by user count alone. Twenty modest mailboxes from webmail is typically a few days of background copying plus a single cutover evening. Large mailboxes or an on-premise Exchange estate take longer. The cutover itself is usually one evening or weekend regardless of the overall length.
helpDo calendars and contacts migrate with IMAP?
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No. IMAP is a mail protocol and carries messages and folders only. Calendars and contacts have to be exported from the source and imported separately, which is straightforward but must be in the plan. Anyone quoting an IMAP migration without mentioning this has not thought about your calendars, and you will find out in the first week.
helpWhich migration method will you use for us?
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It depends on the source. On-premise Exchange below about fifty users is usually a cutover migration; larger estates move in batches through a minimal hybrid; anything that must coexist for months, or keep Exchange on-premise, a full hybrid. cPanel webmail and Zoho Mail go over IMAP. Google Workspace generally warrants dedicated tooling because of the file side. We tell you which method and why in the scope, before you commit.
helpWill we lose email during the migration?
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You should not. Mail is copied into Microsoft 365 and verified against the source while your existing system stays live and authoritative, so nothing hinges on one moment. MX records change only after verification, and a delta sync afterwards picks up anything that arrived during DNS propagation. The old mailboxes also stay readable for an agreed period as a fallback.
helpCan we migrate PST files that are sitting on people's laptops?
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Yes, and it is usually worth doing. A PST on a single laptop is one hard-drive failure from gone, and it is invisible to search, retention and eDiscovery. The technical import is simple; gathering the files is the slow part, because they are rarely where anybody remembers leaving them.
helpWhat happens to email that arrives during the switchover?
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It is delivered to whichever system DNS is currently pointing at, and picked up by the delta sync afterwards. That is exactly why the DNS TTL is lowered in advance — a short TTL shrinks the ambiguous window from most of a day to under an hour, and the delta sync closes it entirely.
helpDo we have to reconfigure everyone's phone?
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Yes. Every device with the old mailbox on it needs its account removed and re-added. We provide short written instructions per device type and schedule the cutover so people arrive to a note explaining what to do, rather than to an inbox that has stopped working with no explanation.
helpWe are moving from Google Workspace specifically.
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That has its own page, because the file side is the interesting part — Google Shared Drives and SharePoint sites do not map one to one, and that is a structural decision rather than a copy job. Our Google Workspace to Microsoft 365 page covers it.
Related pages
Microsoft 365 Migration
The umbrella view: files as well as mail, and the full cutover sequence.
Google Workspace to Microsoft 365
The source-specific version, where the file mapping is the real work.
Microsoft 365 Migration Checklist
The practical before, during and after list — take it and use it.
Microsoft 365 Business Email
How mailboxes, shared addresses and aliases are structured on arrival.
Microsoft 365 Email Security
Authentication and threat protection, which a migration can quietly break.
Microsoft 365 Services
Licensing, implementation, migration, security and support in one place.
Gmail Migration for Business
The equivalent work on the Google side.
Scope your migration
Mailbox count and rough sizes is enough to start.
Scope your email migration
Tell us what you are on today, how many mailboxes, and roughly how large the biggest ones are. That is enough for us to name the method and quote it.
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Method chosen for your source, with the reason stated
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Calendars and contacts handled explicitly, not assumed
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Old mailboxes kept readable for an agreed period after cutover
Moving off a local hosting company’s webmail, or PST files kept on laptops, is covered for Kerala businesses on our page for Microsoft 365 partner in Kerala.
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