Guide
The Complete Guide to IMAP Email Migration
Whether you're an IT administrator migrating thousands of corporate mailboxes or a small business owner switching email providers, this guide walks you through everything you need to know about IMAP email migration.
What is IMAP Email Migration?
IMAP (Internet Message Access Protocol) email migration is the process of copying email messages, folders, and folder structures from one IMAP email server to another. Unlike POP3 — which downloads emails to a single device — IMAP keeps emails synchronized on the server, making it the standard protocol for modern email services.
When you migrate emails via IMAP, you're essentially telling a tool like Mailbox Taxi to connect to your source email server, read all the messages and folders, and then write (upload) them to the destination server. The original emails remain untouched on the source — it's a copy operation, not a move.
This approach works with virtually every email provider: Gmail, Outlook/Office 365, Yahoo Mail, iCloud Mail, Zoho, AOL, ProtonMail (via Bridge), Fastmail, GMX, Yandex, and any server that supports the IMAP protocol, including self-hosted solutions like Dovecot, Zimbra, and hMailServer.
When Do You Need Email Migration?
Email migration is typically needed in these scenarios:
Company-wide provider switch
Your organization is moving from one email platform to another (e.g., on-premise Exchange to Google Workspace).
Server decommissioning
A legacy email server is being retired and all mailboxes need to move to a new platform.
Personal provider change
You're switching from Gmail to Outlook, iCloud to Fastmail, or any other provider combination.
MSP client migrations
Managed service providers migrating multiple client organizations to new platforms.
Before You Start: Pre-Migration Checklist
A successful migration starts with preparation. Run through this checklist before starting any email migration:
Verify IMAP is enabled on both source and destination accounts. Some providers (like Gmail) require you to enable IMAP access in settings.
If using Gmail or Outlook, generate an App Password if two-factor authentication is enabled. Regular passwords won't work with IMAP when 2FA is on.
Check mailbox storage quotas on the destination. Ensure the destination account has enough storage space for all incoming emails.
Document your folder structure. Take note of any custom folders, labels (Gmail), or categories that need to be preserved.
For batch migrations, prepare your CSV file with source and destination credentials for all accounts.
Test connectivity by running Mailbox Taxi's built-in connection test before starting the full migration.
Plan your migration window. For large migrations, consider running them during off-peak hours to minimize impact on email access.
Notify affected users. If migrating company accounts, inform users about the planned migration and any expected downtime.
Step-by-Step Migration with Mailbox Taxi
Step 1: Install Mailbox Taxi
Download Mailbox Taxi for your operating system (Windows, macOS, or Linux) and run the installer. The application requires no server setup, cloud configuration, or admin privileges. It runs as a standard desktop application.
Step 2: Configure source and destination
Open Mailbox Taxi and select your source email provider from the pre-configured list. Then select your destination provider. For each, the app automatically fills in the correct IMAP server hostname, port, and security settings. If you're using a custom IMAP server, select 'Custom IMAP' and enter the server details manually.
Step 3: Enter credentials
Enter your email address and password (or App Password if 2FA is enabled) for both the source and destination accounts. Your credentials are stored locally on your machine using your operating system's encrypted credential storage — they never leave your device.
Step 4: Test the connection
Click 'Test Connection' for both accounts. Mailbox Taxi will verify that it can successfully authenticate and access the IMAP server. If there's an issue (wrong password, IMAP not enabled, firewall blocking), you'll get a clear error message explaining what to fix.
Step 5: Start the migration
Click 'Start Migration' and monitor progress on the real-time dashboard. You'll see per-folder progress, transfer speed, email counts, and estimated time remaining. You can pause the migration at any time and resume later — it picks up exactly where it left off without re-downloading emails.
Step 6: Review and export report
Once complete, review the migration summary showing total emails transferred, any skipped or failed messages, and per-folder breakdowns. Export a detailed PDF or Excel report for your records, compliance requirements, or client deliverables.
Migrating Between Specific Providers
Gmail to Outlook
One of the most common migration paths. Gmail labels are converted to Outlook folders. Ensure IMAP is enabled in Gmail Settings > Forwarding and POP/IMAP. If using Google Workspace with 2FA, generate an App Password through your Google Account security settings. Mailbox Taxi handles the Gmail label-to-folder mapping automatically.
Outlook to Gmail
Outlook folders are mapped to Gmail labels. Note that Gmail has a 25MB attachment size limit — emails with larger attachments will be flagged in the migration report. If migrating from Office 365, use your full email address as the username and an App Password if 2FA is enabled.
Yahoo to Any Provider
Yahoo requires an App Password for third-party IMAP access. Generate one in Yahoo Account Security settings. Mailbox Taxi's pre-configured Yahoo settings handle the correct server addresses and ports automatically.
iCloud to Any Provider
Apple requires an app-specific password for IMAP access. Generate one at appleid.apple.com under Sign-In and Security > App-Specific Passwords. iCloud's IMAP implementation has some unique folder naming conventions that Mailbox Taxi handles transparently.
ProtonMail (via Bridge)
ProtonMail encrypts emails end-to-end, so standard IMAP access isn't available directly. Install ProtonMail Bridge (a free desktop app from ProtonMail) which provides local IMAP access on localhost. Configure Mailbox Taxi to connect to the Bridge's local IMAP server using the credentials Bridge provides.
Custom / Self-Hosted Servers
For servers running Dovecot, Zimbra, hMailServer, Postfix, or other IMAP implementations, select “Custom IMAP” in Mailbox Taxi and enter your server hostname, port (typically 993 for SSL or 143 for STARTTLS), and security protocol. Contact your server administrator if you're unsure about the correct connection details.
Batch Migration for IT Teams
For organizations migrating multiple mailboxes, Mailbox Taxi supports CSV batch import. This is designed for IT teams, managed service providers, and consultants handling large-scale migrations.
Preparing your CSV file
Create a CSV file with columns for source email, source password, destination email, destination password, source provider, and destination provider. Mailbox Taxi provides a downloadable CSV template with the correct column headers and example rows.
Running a batch migration
Import your CSV file into Mailbox Taxi. The app validates all entries, checks for formatting issues, and lets you test connections for all accounts before starting. Once validated, start the batch migration and monitor all jobs on the live dashboard. Mailbox Taxi runs migrations in parallel — the number of concurrent jobs is configurable based on your network bandwidth and system resources.
Monitoring and reporting
The dashboard shows real-time status for every migration job: queued, in progress, paused, completed, or failed. Once all jobs complete, generate a consolidated report covering every mailbox in the batch for audit trails or client deliverables.
Handling Common Issues
Authentication failed
Double-check your credentials. If 2FA is enabled, you need an App Password — not your regular password. For Gmail, ensure IMAP is enabled in settings. For Yahoo, generate an app-specific password.
Connection timed out
Verify the IMAP server hostname and port are correct. Check that your firewall or VPN isn't blocking IMAP traffic (ports 993 or 143). Try temporarily disabling your VPN to test.
Migration is slow
Speed depends on your internet connection, the number and size of emails, and the email server's rate limits. Some providers (especially Gmail) throttle IMAP connections. Reduce the number of parallel jobs if you're hitting rate limits.
Some emails weren't migrated
Check the migration report for specific error details. Common causes include: emails exceeding the destination's size limit, corrupted messages on the source server, or temporary server errors. You can re-run the migration — Mailbox Taxi skips already-transferred emails.
Folder structure looks different
Different email providers use different folder naming conventions (e.g., Gmail uses labels, Outlook uses folders). Mailbox Taxi maps between these automatically, but some provider-specific folders (like Gmail's 'All Mail') may not have a direct equivalent.
Network interruption during migration
Mailbox Taxi automatically saves progress. Simply resume the migration after your connection is restored — it continues from the last successfully transferred email without duplicating anything.
Post-Migration Verification
After migration completes, verify the results before considering the job done:
- Log into the destination email account and spot-check inbox, sent, drafts, and custom folders.
- Compare email counts between source and destination for each major folder.
- Verify that email dates, subjects, and attachments are preserved correctly.
- Check the migration report for any flagged or skipped messages and address them.
- For batch migrations, review the consolidated report and confirm all mailboxes completed successfully.
- Keep the source account active for a transition period in case anything was missed.
Best Practices & Tips
Use a stable connection
Wired ethernet is more reliable than Wi-Fi for large migrations. If using Wi-Fi, stay close to your router.
Migrate during off-hours
Run large migrations during nights or weekends to avoid competing with normal email traffic.
Don't delete source data early
Keep the source account intact for at least 2 weeks after migration. This gives you a safety net.
Export your reports
Always download the PDF or Excel migration report. It's your proof of successful transfer.
Tune parallel jobs
Start with 2-3 parallel jobs and increase if your connection handles it well. Too many can trigger rate limits.
Communicate with users
For company migrations, give users a timeline, explain what to expect, and provide a contact for questions.