A 5-minute walkthrough of moving Kerio Connect mailbox data directly into a Gmail or Google Workspace account, without producing a PST archive in between. Useful for SMBs that are retiring on-premises Kerio and going cloud-first with Workspace. If you also need to keep a PST archive copy, see our companion guide on exporting Kerio Connect mailbox to PST format.
Video Transcript
Hello and welcome. This video shows how to import Kerio mail server data directly to a Gmail or Google Workspace account, with no PST intermediate step. We use the 4n6 Kerio to Gmail Converter for this walkthrough. Before we start, GFI does not provide an official tool for migrating data out of Kerio Connect, so a third-party tool is required.
The destination must be a Google Workspace account if you are migrating a custom domain, because personal Gmail does not accept inbound IMAP imports for custom-domain mail.
Step one. Generate an app password for the destination Gmail or Workspace account. Sign in to myaccount.google.com, click Security, ensure Two-Step Verification is on, then go to App passwords and create a 16-character password. Copy it.
Step two. Stop the Kerio Connect server briefly, copy the user mailbox folders from the Kerio Store directory to a Windows workstation, then restart Kerio so users keep getting mail.
Step three. Download and install the 4n6 Kerio to Gmail Converter on the Windows workstation. The tool is a standalone Windows application and does not require Kerio Connect or any Google client.
Step four. Launch the tool. Click Add Folders and browse to the copied Kerio user mailbox. The tool reads each #msgs subfolder and shows the folder tree on the left. Tick the folders you want to migrate.
Step five. From the Save As dropdown, pick Gmail or Google Workspace. Enter the destination Gmail address and paste the 16-character app password. For multi-user migrations, tick I am converting Multiple Users and provide a CSV mapping of source folder to destination email.
Step six. Click Convert. The tool uploads each EML message to the destination Gmail mailbox via IMAP. A live progress bar shows uploaded count. When complete, a Notepad log lists items migrated, items skipped, and any errors. Verify by opening the Gmail account and checking that folders now appear with the correct message count. Thanks for watching.
Why This Migration Needs a Third-Party Tool
GFI's official Kerio Connect documentation states this directly: in the article Migrating Content from Kerio Connect to Another Platform, GFI confirms that "there is no official tool for migrating content out of Kerio Connect. All migration tools were developed for bringing content into Kerio Connect." GFI's support team explicitly cannot help with outbound migrations because it falls outside their support scope.
This leaves three realistic options for moving Kerio data to Gmail / Google Workspace: a third-party migration tool that uploads directly to Gmail via IMAP (this video), the Kerio Outlook Connector to assemble a PST first then ingest the PST into Workspace, or use Google's built-in Workspace Data Migration Service with Kerio configured as an IMAP source. The cloud-direct path covered here is the fastest for active migrations because messages start appearing in Gmail as the upload progresses, with no PST file to wait on.
The tool used in this video is the 4n6 Kerio to Gmail Converter, a Windows desktop application that reads the Kerio Store directory tree directly and uploads messages to a Gmail or Workspace mailbox via IMAP. This is a different product from the 4n6 Kerio Server Converter covered in our companion Kerio to PST guide: that tool is for producing PST archives, this one is for direct cloud upload.
Cloud-Direct vs PST-Intermediate Path
Both paths get Kerio data into Gmail. They differ on speed, archive availability and what can go wrong.
| Path | When to pick it |
|---|---|
| Cloud-direct (this video) | Pick when you are actively retiring Kerio and need messages live in Workspace as fast as possible. Uses 4n6 Kerio to Gmail Converter. Uploads EML files directly to Gmail via IMAP. Messages appear in Gmail as upload progresses. No PST file produced. Pros: faster for active migrations, no intermediate disk space needed. Cons: depends on stable internet through the entire upload, no archive copy unless you keep the original Kerio Store. |
| PST intermediate (companion guide) | Pick when you also want a portable archive copy, or when the target Workspace account is not yet ready. Uses 4n6 Kerio Server Converter. Produces PST files first, then upload PSTs to Workspace separately via Google Workspace Data Migration Service. Pros: archive copy preserved, can run upload separately when network is stable. Cons: slower for live migration, needs disk space for PSTs. See our Kerio to PST guide. |
| Workspace Data Migration Service (DMS) with Kerio IMAP source | Pick when Kerio is still actively running and IMAP is enabled. Configure Kerio as an IMAP source in admin.google.com > Data Migration. Pros: free, no third-party tool. Cons: requires live Kerio with IMAP, has a 2,500 messages-per-user-per-session ceiling, calendars and contacts handled separately, slow on large mailboxes. |
| Kerio Outlook Connector + Outlook PST + Workspace import | Free fallback path: install Kerio Outlook Connector, sync each user's mailbox into Outlook to produce a PST, then import PSTs to Workspace via Outlook configured with the destination Workspace account. Cons: per-user manual work, slow, doesn't preserve some metadata. Mostly suitable when you only have a few mailboxes. |
Pre-Migration Checklist
Cloud migrations fail more often from configuration mistakes than from tool problems. Work through this list before clicking Convert.
| Check | Why it matters |
|---|---|
| Workspace account purchased and licensed | Each user being migrated needs a Workspace license assigned in admin.google.com. Migrating to an unlicensed mailbox produces silent IMAP failures. |
| Custom domain verified in Workspace | If your Kerio email is on yourname@yourcompany.com, verify yourcompany.com in Workspace admin first. Workspace will not accept IMAP uploads to unverified domain users. |
| 2-Step Verification enabled per user | App passwords are gated behind 2FA. Without 2FA enabled on the destination user, the App passwords page does not appear. See our Gmail app password guide. |
| App password generated per destination user | One 16-character app password per destination mailbox. Copy each immediately, you cannot view it again later. Name them descriptively like "Kerio Migration 2026". |
| Workspace IMAP enabled | Workspace IMAP is on by default but can be disabled by an admin policy. Verify in admin.google.com > Apps > Google Workspace > Gmail > End User Access. IMAP must be on for the destination users. |
| Kerio Store folder copied off the live server | Stop Kerio Connect briefly, copy the Store/Mail/<domain>/ folder to a Windows workstation, restart Kerio. Reading a live Store while Kerio is writing produces truncated EML files. |
| Stable internet connection | Cloud migration uploads every EML message over the network. A 50 GB mailbox needs 50 GB of upload time. On 50 Mbps Indian residential broadband, that's roughly 2.5 hours sustained. Run the migration on wired ethernet, not Wi-Fi. |
| MX records still pointing at Kerio | Do NOT switch MX records before migration completes. Mail flow stays on Kerio during migration so no incoming messages are lost. MX cutover happens after. |
| Trial run with one user first | Migrate one small volunteer mailbox end-to-end. Verify message count, folder structure, attachments, calendar items. Only then start the bulk migration. |
| Communicate with users | Tell affected users that mail flow will be moved during a specific maintenance window. Schedule the MX cutover for an off-hours period like 11pm Friday. Most Indian SMBs prefer weekend cutovers so Monday morning users come in to a fully working Workspace. |
Tool Requirements
| Requirement | Value |
|---|---|
| Tool name | 4n6 Kerio to Gmail Converter |
| Vendor | 4n6 Software (forensiksoft.com) |
| Trial limit | 10 messages per folder, free download |
| Operating system | Windows 7 / 8 / 10 / 11 (32 or 64-bit), Windows Server 2008 / 2012 / 2016 / 2019. The migration tool is Windows-only even though the source Kerio Connect runs cross-platform. |
| Source Kerio Connect versions | Kerio Connect 7.x, 8.x, 9.x, 10.x. All GFI Kerio Connect releases. |
| Source Store access | Read access to the Kerio Store/Mail/<domain>/<user>/ directory tree. Local copy, network share or USB drive all work. |
| Destination | Gmail (@gmail.com personal account, only if migrating from a similar personal-account source) or Google Workspace (custom-domain account, the typical SMB destination). |
| Destination authentication | 16-character Gmail/Workspace app password. Generate at myaccount.google.com/apppasswords after enabling 2-Step Verification. |
| Internet | Required throughout the upload. Plan for sustained upload bandwidth. Wired ethernet recommended over Wi-Fi for stability. |
| Disk space (workstation) | Just enough to hold the copy of the Kerio Store. PST output is not produced in this workflow, so no extra archive disk needed. |
| RAM | 4 GB minimum, 8 GB for large mailbox uploads. |
Gmail and Workspace IMAP Settings (Destination)
The 4n6 tool uploads via IMAP to Google's servers. These are the settings the tool uses. Worth knowing in case authentication fails.
| Setting | Value |
|---|---|
| IMAP server | imap.gmail.com |
| Port | 993 with SSL/TLS required |
| Username | Full destination email address (yourname@yourcompany.com for Workspace, yourname@gmail.com for personal) |
| Password | 16-character app password, NOT the regular Google account password |
| Authentication | PLAIN over SSL. The tool handles this automatically |
| Source documentation | Settings published by Google at Check Gmail through other email platforms. Same settings apply for Workspace |
6 Steps to Import Kerio Mail to Gmail Account
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Generate a Gmail or Workspace app password. Sign in to the destination account at myaccount.google.com. Click Security. Ensure 2-Step Verification is on. Go to myaccount.google.com/apppasswords. Create a new app password named for this migration ("Kerio Migration 2026" works). Copy the 16-character code immediately, you cannot view it again later. For multi-user migrations, generate one app password per destination user. See our Gmail app password guide for screenshots.
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Copy the Kerio Store folder to a Windows workstation. On the Kerio server, stop the Kerio Connect service for the copy (services.msc on Windows, sudo systemctl stop kerio-connect on Linux). Copy the user mailbox folders from Store\Mail\<domain>\ to your Windows workstation. Restart Kerio Connect after the copy completes so users keep getting mail during the upload phase. The migration runs against the copy, not the live store.
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Install the 4n6 Kerio to Gmail Converter. Visit forensiksoft.com and download the installer. Install on the Windows workstation. The tool is standalone, takes about 2 minutes to install, and does not require Kerio Connect, Outlook or any Google client to be present.
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Load the Kerio mailbox and select folders. Open the converter. Click Add Folders and browse to the copied Kerio user mailbox at Store\Mail\<domain>\<user>\. The tool walks each #msgs subfolder, parses every .eml file, and displays the folder tree on the left panel: INBOX, Sent Items, Drafts, custom folders, MyContacts, MyCalendar, MyTasks, MyNotes. Tick the checkboxes next to folders you want to migrate.
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Pick Gmail and enter destination credentials. From the Save As dropdown, pick Gmail or Google Workspace (both options route through imap.gmail.com). Enter the destination email address. Paste the 16-character app password from step 1. For multi-user migrations, tick I am converting Multiple Users and provide a CSV file mapping source mailbox folder paths to destination email addresses.
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Click Convert and verify in Gmail. Click Convert. The tool uploads each EML message to imap.gmail.com port 993 SSL using the app password. A live progress bar shows uploaded count. When complete, a Notepad log lists items migrated, items skipped, and any errors. Sign in to the destination Gmail account in a browser and verify the folder structure and message counts match the source Kerio mailbox.
Common Errors and Fixes
| Error or symptom | Cause and fix |
|---|---|
| "Invalid credentials" / authentication failed | You used the regular Google account password instead of an app password. Or the app password was copied with a trailing space. Or 2FA was disabled on the destination account, which silently invalidates app passwords. Generate a fresh app password and paste it carefully into the tool. The 16-character format has no spaces. |
| "Access for less secure apps" warning | Outdated. Google removed the Less Secure Apps setting in May 2022. App passwords are now the only IMAP login path. If a tool prompts for "less secure apps", it is reading old documentation. Use the app password as the password. |
| Upload starts then stalls after a few hundred messages | Hit Gmail's rate limit. Workspace allows roughly 10,000 IMAP messages per day per user. Personal Gmail allows less. The tool throttles automatically and resumes, but may pause for several minutes between batches. Run overnight for large mailboxes. |
| Folders appear in Gmail but with zero messages | The tool created the folder structure via IMAP CREATE but the actual upload of message bodies failed silently. Check the conversion log for skipped items. Often caused by a single malformed EML in Kerio causing the parser to abort that folder. Skip the corrupt file and re-run. |
| Custom domain destination rejects upload | Workspace domain not yet verified, or the destination user not yet licensed. Sign in to admin.google.com, verify the domain via DNS TXT record, assign a Workspace license to the destination user, then retry the migration. |
| Calendar items appear in Inbox instead of Calendar | The MyCalendar folder was treated as a mail folder by the tool. Run the conversion separately for MyCalendar with output set to ICS, then import the resulting ICS file into Google Calendar at calendar.google.com > Settings > Import & Export. |
| Contacts appear scattered as individual emails | MyContacts was uploaded as mail. Re-run for MyContacts with output set to vCard (.vcf) or CSV, then import into Google Contacts at contacts.google.com > Import. |
| Connection drops mid-migration | Indian residential broadband is often unstable for sustained uploads. Run the tool with a wired ethernet connection. If drops continue, split the migration into per-folder batches so a single disconnect does not lose hours of progress. The tool does not always resume cleanly, so smaller batches mean smaller restarts. |
| Workspace storage full | Workspace Business Starter has 30 GB per user, Business Standard has 2 TB per user, Business Plus has 5 TB. Check your plan's storage quota before migration. If a Kerio mailbox is 50 GB but the user is on Business Starter (30 GB), the migration cannot complete. Upgrade the user's plan first. |
| Some messages migrated, others skipped without explanation | Gmail rejects messages over 50 MB. EML files in the Kerio Store with attachments larger than this limit will skip silently. Check the log for "size exceeded" entries. For these messages, extract attachments separately and re-upload via Gmail's web interface or Google Drive. |
MX Record Cutover Plan
The mail-flow cutover from Kerio to Workspace is the riskiest part of the project. Get this wrong and incoming mail to your domain bounces for hours. The plan below works for a typical SMB cutover.
| Phase | What happens |
|---|---|
| Before migration | MX records point to Kerio. All mail flows to Kerio. Users still working in Kerio webmail / Outlook Connector. Migration tool uploads historical mail to Workspace mailboxes in parallel. No mail flow change yet. |
| Migration in progress | Run the 4n6 Kerio to Gmail Converter for all users. This typically takes hours to days depending on mailbox sizes and bandwidth. Mail still flowing to Kerio during this period. Plan to run it on a Friday so it finishes by Sunday. |
| Verification phase | After migration completes, sign in to each Workspace mailbox. Verify message count matches source. Verify folder structure. Verify a few key recent emails. Have the user themselves verify if possible. Do not proceed to MX cutover until verification passes. |
| MX cutover | Update DNS MX records at your registrar. Set the primary MX to ASPMX.L.GOOGLE.COM with priority 1, plus the four secondary MX records (ALT1.ASPMX.L.GOOGLE.COM through ALT4.ASPMX.L.GOOGLE.COM) per Google's official Workspace MX setup. Set TTL low (300 seconds) a day before to speed propagation. |
| Cutover window | For 24-48 hours after MX change, mail can land at either Kerio or Workspace as DNS propagates. Configure Kerio to forward all incoming mail to the Workspace domain during this window so nothing is lost. After full propagation, mail flows only to Workspace. |
| Post-cutover | Keep Kerio running read-only for 30-90 days as a safety net. Users should be on Workspace exclusively. Once you're confident no missed messages remain in Kerio, decommission Kerio Connect. |
Tool Comparison: Kerio to Gmail Migration Options
| Tool | Notes |
|---|---|
| 4n6 Kerio to Gmail Converter (this video) | $99 personal / $299 business / $499 enterprise. Direct cloud upload via IMAP. Trial: 10 messages per folder. Windows only. Bundled with sister product 4n6 Kerio Server Converter (PST output) and 4n6 Kerio to Office 365 Migration (Microsoft 365 destination). |
| Google Workspace Data Migration Service (DMS) | Free, included with Workspace. Configured at admin.google.com > Data Migration. Supports IMAP source. Pros: free, official, no third-party software. Cons: 2,500 messages per user per session ceiling per Google's DMS documentation, requires live Kerio with IMAP enabled, calendars and contacts handled separately. Best for small migrations under 10,000 messages. |
| RecoveryTools Kerio Migrator | Similar pricing range. Strong cloud destination support including Workspace, Office 365, Yahoo, Outlook.com. Trial: 25 messages per folder. Windows only. |
| BitRecover Kerio Converter | ~$89 starter price. 25+ saving formats including direct Workspace upload. 30-day money-back guarantee. Trial: 25 messages per folder. |
| Transend Migrator (Kerio to Workspace) | Enterprise-focused. Documented in Transend's Kerio to Google Workspace migration scenario. Higher price. Used by IT consultancies for enterprise migrations with parallel processing across multiple machines. |
| SysTools (no dedicated Kerio-to-Gmail product) | SysTools does not ship a dedicated Kerio Connect to Gmail migration tool. Their closest match is the SysTools IMAP Migration tool, which works when Kerio is still running with IMAP enabled. Picked when the source server is live and IMAP-accessible; not suitable when only a Store folder backup is available. |
Real Migration Scenarios
| Scenario | Approach and notes |
|---|---|
| SMB retiring on-premises Kerio Connect, moving to Workspace Business Standard | The most common case. ~10-50 user mailboxes, total 30-200 GB. Cloud-direct migration with the 4n6 tool. Plan for one weekend of upload work. Key prerequisite: domain already verified in Workspace and licenses assigned to all destination users. |
| Domain rebrand: Kerio on yourcompany.com, Workspace on newcompany.com | Less common but tricky. Migration tool can map source folder to a different destination email address via the CSV mapping feature. Set up email aliases on the new domain so Kerio mail addressed to old@yourcompany.com lands as new@newcompany.com. Test the mapping with one user before bulk. |
| Kerio on Linux server, Workspace destination | Common in mixed-OS Indian SMBs. Copy the Kerio Store from /opt/kerio/mailserver/store/mail/ to a Windows workstation via scp, rsync or USB drive. EML format is portable across operating systems so no path translation is needed. Migration tool runs on Windows side. |
| Hybrid period: some users on Kerio, others on Workspace | For phased migrations, split the user list. Migrate IT and management first, then operations, then sales. During the hybrid period, set up Kerio aliases to forward mail for migrated users to their new Workspace addresses. MX cutover happens after everyone is migrated. |
| Departed-employee archive into a shared Workspace mailbox | When an employee leaves, migrate their Kerio mailbox into a shared Workspace mailbox kept by HR or the manager. Use the CSV mapping feature to point all source folders at the shared destination address. Allows compliance access without paying for a full per-user license long-term. |
| Migration to G Suite Legacy free edition (existing accounts only) | The free G Suite Legacy edition was discontinued for new signups in 2012 but existing accounts continued until 2022. If you still have a legacy free Workspace, the migration steps are identical, but storage limits are tighter (15 GB per user vs Workspace Business 2 TB). Verify quotas before migration. |
đź’ˇ Pro tips for Kerio to Gmail migrations
- Run migration before MX cutover, not after. Historical mail uploads while Kerio still receives new mail. Once everything is in Workspace and verified, then cut over MX. This minimises lost or bouncing messages.
- Use one app password per destination user, named descriptively. "Kerio Migration 2026 user1@example.com" works. After migration completes, revoke each app password from myaccount.google.com/apppasswords. Leaving them active is a credential sitting around for no reason.
- Schedule for off-hours. Most Indian SMBs prefer Friday-night start so the upload runs over the weekend and Monday morning users are on Workspace. Avoid Monday or Tuesday cutovers, you have less time to fix issues before the working week ramps up.
- Wired ethernet for the workstation running migration. Wi-Fi on Indian residential broadband regularly has 5-30 second drops that can break the IMAP session. Wired connection is significantly more reliable.
- Forward Kerio mail to Workspace during MX propagation. Configure Kerio to send a copy of all incoming mail to user@yourcompany.com (the Workspace mailbox) during the 24-48 hour DNS propagation window. This guarantees no messages are missed regardless of which server DNS resolution lands on.
- Verify per-user counts before users are told to switch. Compare message count in Kerio webmail to message count in Workspace inbox for each migrated user. Even a small discrepancy is worth investigating before the user starts working in Workspace.
- Handle MyCalendar and MyContacts separately. The 4n6 tool handles them in the same pass but the resulting Gmail-side rendering depends on whether the tool detects them as calendar/contact sources. Verify in Google Calendar and Google Contacts after migration. Re-run with ICS / vCard output if needed.
- Keep the Kerio Store folder for 90 days minimum. If a user reports missing email after migration, you can re-extract from the original Store and uppload those specific messages to the user's Workspace mailbox.
- If your destination is Microsoft 365 instead of Workspace, use the 4n6 Kerio to Office 365 Migration product instead. Same source, different destination.
- If you also need a PST archive copy, see our Kerio Connect to PST guide. Run that conversion alongside or after the cloud migration to keep a portable backup.
Frequently Asked Questions
Why is a third-party tool needed for Kerio to Gmail migration?
GFI's official Kerio Connect documentation explicitly states there is no official tool for migrating content out of Kerio Connect. All Kerio migration tools were built for migrating into Kerio. To go the other direction (Kerio to Gmail, Office 365, or any other destination), a third-party tool is required. The 4n6 Kerio to Gmail Converter handles this case by reading the Kerio Store directory directly and uploading messages to Gmail via IMAP.
Personal Gmail or Google Workspace as destination?
For migrating a custom-domain Kerio mailbox (yourname@yourcompany.com), the destination must be a Google Workspace account on the same custom domain. Personal Gmail (@gmail.com) does not accept inbound IMAP imports for custom-domain mail. If the source Kerio account is already on @gmail.com style addresses, personal Gmail works as the destination, but most Kerio Connect deployments use custom domains, so Workspace is the realistic target.
Do I need to install Kerio Connect to use the converter?
No. The 4n6 Kerio to Gmail Converter is a standalone Windows application. It reads the Kerio Store directory contents directly without needing Kerio Connect server software installed. Most migrations involve copying the Kerio Store folder from a server to a separate Windows workstation where the conversion runs.
What is the difference between Kerio to Gmail and Kerio to PST then PST to Gmail?
The cloud-direct path (this video) uploads EML messages from the Kerio Store directly to Gmail via IMAP, with no PST file in between. It is faster for active migrations because messages start appearing in Gmail as the upload progresses. The PST intermediate path produces a portable PST file you can keep as an archive, then upload to Gmail in a second step. Pick cloud-direct for live migrations to Workspace, pick PST intermediate when you also need a long-term archive copy. See our companion Kerio to PST guide.
What are Gmail and Workspace IMAP migration limits?
Personal Gmail allows roughly 35 MB upload per IMAP session and a few hundred messages per minute. Workspace permits higher quotas. Google's official Workspace Data Migration Service (DMS) has a 2,500 messages-per-user-per-session ceiling. The 4n6 tool does not use DMS, it uploads directly via IMAP, but it does respect Google's rate limits to avoid temporary lockouts. For 10,000+ message mailboxes, expect 30 minutes to several hours per user.
Should I cut over MX records before or after migration?
After. Run migration first while Kerio is still receiving mail, so the mail flow does not stop. Once all historical mail has uploaded to Workspace and you have verified message counts, schedule a maintenance window to update DNS MX records pointing to Google's MX servers (ASPMX.L.GOOGLE.COM and the secondary records). DNS propagation typically takes 1-4 hours but can be longer. During cutover, mail can still be delivered to either Kerio or Workspace, so plan to forward newly received Kerio mail to Workspace mailboxes for the first 48 hours.