Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. Moving mailboxes from Kerio Connect to Exchange Server splits by what you need to keep. For mail alone, a free IMAP migration through imapsync or Exchange’s own batch does the job. For calendars, contacts and tasks as well, IMAP is not enough, so route those through a PST or a migration tool that can read the Kerio data directly.
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What decides the route?
Kerio Connect to Exchange Server is a normal server to server migration, and despite what some guides claim there are genuine free ways to do it. The right one depends on a single question, are you moving only the mail, or the calendars, contacts and tasks as well.
That distinction runs through everything below because of how the transport works. Mail moves cleanly over IMAP, which both Kerio and Exchange speak, and that path is free. Groupware items do not travel over IMAP at all, so if you need them in Exchange you take a different route, usually through a PST. Sort out which of the two you need and the method almost picks itself.
Two roads to the same server. What you carry decides which.
“The trap in any Kerio to Exchange move is treating it as one job when it is really two. IMAP will carry the mail faithfully and it costs nothing, but it has no concept of a calendar entry or a contact card, so those simply will not appear on the other side. When they matter you have to stage them through a PST. And if the Kerio server itself is already gone, the useful thing to know is that its stored data can be read straight off the file, which is often the only route left.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
The free way for mail, IMAP migration
If mail is all you need in Exchange, you do not have to buy anything. Two free routes both work.
imapsync. The free, open source tool imapsync copies mail from one IMAP server to another, so it moves each Kerio mailbox straight into its Exchange counterpart. You give it the Kerio and Exchange hosts and the account credentials, and it syncs the folders across. Both servers need IMAP enabled and reachable while it runs.
Exchange’s own IMAP migration. Exchange has this built in. In the Exchange Admin Center, go to migration, choose to migrate to Exchange, and pick IMAP migration. You supply a CSV list of users and a migration endpoint pointing at the Kerio IMAP server, and Exchange pulls the mail in as a batch. It is the natural choice when you are moving many mailboxes at once and want it managed from the Exchange side.
Both are free and both move mail well. The catch is the same for each, and it is the whole reason for the next section.
Carrying calendars and contacts too
IMAP carries mail only. Calendars, contacts and tasks are groupware items, and the IMAP protocol has no way to move them, so an IMAP migration quietly leaves them behind. If your users need their calendars and address books in Exchange, plan for those separately.
The dependable route is through a PST. Configure the Kerio account in Outlook, ideally with the Kerio Outlook Connector so the calendar and contacts come across as well as the mail, then export that mailbox to a PST. From there you import the PST into the Exchange mailbox, which on an on premises Exchange Server is done with the built in import request. Our guide to import a PST to Exchange Server covers that final step, and there is a dedicated walkthrough to export a Kerio mailbox to PST for the first half.
IMAP is a mail pipe. Groupware needs the PST route instead.
When the Kerio server is gone, a tool
The free routes above assume both servers are live. If the Kerio server has already been decommissioned and you are left with its stored data, or you simply want to push many mailboxes across without setting up IMAP on each source account, a migration tool reads the Kerio data directly. The PCDOTS Kerio Converter loads Kerio mailboxes, including orphaned files with no configured account behind them, and sends the mail into Exchange over IMAP in bulk. Being honest about what that means, because it delivers over IMAP the tool moves mail, the same scope as the free routes, so its real value is reading the Kerio store when there is no live server and handling many mailboxes in one pass rather than one by one. For calendars and contacts you would still take the PST route above. There is a free demo that migrates ten files per folder so you can test it on your own data first.
The tool route, for orphaned Kerio data or a large batch.
Here are the steps with the screens.
Step 1. Install and run the migrator on Windows, then open the menu.
Step 2. Choose Email Servers and load your Kerio files or folder.
Step 3. Open the Export menu and select IMAP.
Step 4. Enter your Exchange Server login and start the migration.
If your destination is actually Microsoft 365 rather than an on premises server, the same ideas apply but there is a separate guide to migrate Kerio to Office 365.
The methods compared
Match the route to what you are carrying and whether both servers are still live.
| Method | Best for | Good to know |
|---|---|---|
| imapsync or Exchange IMAP migration | Mail, both servers live, free | Mail only, no calendar or contacts |
| PST route | Mail plus calendar and contacts | Via Outlook, then import to Exchange |
| Kerio Converter tool | Orphaned store or a large batch | Reads Kerio files, mail over IMAP |
Frequently asked questions
Is there a free way to migrate Kerio to Exchange Server?
Yes. For mail, imapsync copies each mailbox over IMAP, and Exchange has a built in IMAP migration batch in the Exchange Admin Center. Both are free and both move mail.
Will my calendars and contacts move over IMAP?
No. IMAP carries mail only. To bring calendars, contacts and tasks into Exchange, export the Kerio mailbox to a PST through Outlook and import that PST into the Exchange mailbox.
How do I migrate if the Kerio server is already gone?
Use a tool that reads the Kerio stored data directly, including orphaned files, and sends the mail into Exchange. That works without a live Kerio server, which the free IMAP routes need.
Does this work with Exchange Online and Microsoft 365?
The IMAP idea is the same, but Microsoft 365 uses its own import service for some steps. There is a separate guide for migrating Kerio to Office 365 if that is your target.
Which Exchange versions does this cover?
Any modern on premises Exchange Server, since the mail arrives over standard IMAP and any PST is brought in with the built in import request.
Can I move many mailboxes at once?
Yes. Exchange’s IMAP migration takes a CSV of users for a batch, and a migration tool can process many Kerio mailboxes in one pass.
It comes down to more than the mail
The mail itself is the easy part. imapsync or Exchange’s own IMAP migration will move it across for nothing, and a tool will do the same from an orphaned Kerio store when the server is gone. The real decision is everything around the mail. If your users also expect their calendars and contacts waiting for them in Exchange, IMAP alone will disappoint them, and the PST route is what keeps those together. So before you start, the question worth answering is not how to move the mail, but whether the calendars and contacts need to land with it.
