T-Online to Office 365 Email Migration
Move T-Online / Telekom Mail email to Microsoft 365 using a provider-specific IMAP connection. Telekom currently documents secureimap.t-online.de as the IMAP server, port 993, with SSL/TLS.
For external email programs, Telekom requires a separate password for email programs rather than the normal Email Center login password. Use the full @t-online.de or @magenta.de email address together with that email-program password.
EdbMails IMAP Migration Tool supports single and bulk mailbox connection, mapping, selective migration, concurrent processing, incremental follow-up runs, and migration reports. Standard IMAP migrates supported email/mail folders rather than contacts, calendars, tasks, or other non-mail workloads.
Use this provider-specific page together with the main IMAP to Office 365 migration guide for destination-wide Microsoft 365 prerequisites, authentication, mapping, and cutover planning.
User Query
"Our business has been relying on T-online for email, but we now need more storage, stronger security, and seamless integration with other productivity tools. We’re considering moving to Office 365. Could you offer a straightforward, trustworthy, and secure solution for migrating our T-online emails to Office 365?" - Jhon, Melbourne.
Comparison of T-Online emails and Office 365 Features
| Area | T-Online / Telekom Mail | Microsoft 365 |
|---|---|---|
| Source access | secureimap.t-online.de | Current EdbMails Microsoft 365 target connection |
| Authentication | Full email address plus Telekom email-program password | OAuth-based Microsoft 365 authentication |
| IMAP migration scope | Email messages and mail folders available through IMAP | Supported email data written to the target mailbox |
| Non-mail data | Contacts/calendars are outside standard IMAP | Handle separately if required |
T-online email to Office 365 Migration Plan
- Inventory T-Online/Telekom mailboxes, mailbox sizes, folders, aliases, and active users.
- Confirm that each source account has the required Telekom password for email programs.
- Use secureimap.t-online.de, port 993, SSL/TLS, with the full email address.
- Create/provision Microsoft 365 target mailboxes and assign licenses.
- Add and verify the custom domain in Microsoft 365 if it will be used for production mail.
- Review source connection limits, Microsoft 365 throttling, message-size policies, and bandwidth.
- Run a pilot mailbox and verify the target before the production batch and DNS cutover.
Pre-migration Steps for T-online email to Office 365
T-Online / Telekom source
- IMAP server: secureimap.t-online.de.
- Port: 993.
- Security: SSL/TLS.
- Username: full T-Online/Telekom email address.
- Password: Telekom password for email programs.
- For bulk migration, prepare the EdbMails CSV and validate a small test set first.
Microsoft 365 target
- Create/provision target mailboxes and assign licenses.
- Add and verify the custom domain if required.
- Use the current EdbMails OAuth-based Microsoft 365 target connection.
- Run a pilot before production migration.
Steps to Migrate emails from T-online to Office 365
Step 1: Download and install EdbMails IMAP migration software
- Start by downloading EdbMails and installing it on a Windows environment listed in the current system requirements.
See a detailed list of EdbMails system requirements for IMAP migration.
- Launch the EdbMails application on your system.
- Enter your registered email address and password, then click ‘Login’. If you’re using EdbMails for the first time, choose ‘Start Your Free Trial’ to proceed with the trial version.Note: The EdbMails IMAP trial lets you evaluate the workflow and migrate up to 30 items from each folder. To migrate all eligible items for licensed mailboxes, purchase the required IMAP migration license.
- Select the option ‘IMAP (Gmail, Outlook & more) Migration’.
- Select ‘IMAP to Office 365 Migration’.
- You can continue with the default job name provided by EdbMails or select ‘New Job’ to assign a custom name. This allows you to organize multiple migration tasks more efficiently and makes it easier to identify, track, and manage each migration job.
- Start by downloading EdbMails and installing it on a Windows environment listed in the current system requirements.
Step 2: Connect to the source T-online email server
- To connect a single T-Online mailbox, select ‘Single User / Account Migration’, choose ‘Connect to IMAP Server’, and click ‘Next’.
- Click ‘Next’ to proceed.
- Enter secureimap.t-online.de as the IMAP server, use port 993 with SSL/TLS, and provide the full T-Online/Telekom email address together with the Telekom password for email programs.
- Enter the email address and password in the required fields.
- For T-Online/Telekom, use the dedicated password for email programs. Do not use Gmail app-password instructions for this source account.
- Click the ‘Login’ button to proceed.
- To connect multiple T-Online mailboxes, select ‘Multiple (Bulk) Users/Accounts Migration’, choose ‘Connect to IMAP Server’, and click ‘Next’.
- Click ‘Next’ to continue.
- Click ‘IMAP Migration CSV File’. It will load the sample CSV file to your local drive.
- Open the CSV file and fill in the necessary details, including the email address, password, IMAP server hostname, and port number for each mailbox. After completing the entries, save and close the updated CSV file.
- After updating the CSV file, save it and close it.
- Then, click the 'Load Modified CSV File' button, open the updated CSV file and click ‘Next’ to proceed.
- Choose one or more mailboxes or specific folders you wish to migrate.
- Then click ‘Next’ to continue with migration.
Step 3: Connect to target Office 365 server
- Click the ‘Add New Connection’ button to create a new connection to your target Office 365 server. To use an existing connection, simply select it from the list and click ‘Connect to Existing’ to continue.
- Select the Microsoft 365 mailbox connection option appropriate for the destination mailbox used for this IMAP email migration, then continue with the current EdbMails OAuth-based authentication workflow.
- Choose the necessary connection options and click ‘Next’ to continue with authentication methods.
- Choose your preferred secure authentication method for the target Office 365.
- The login process takes place on the official Microsoft sign-in page, where your credentials are securely authenticated through OAuth 2.0, ensuring a safe and protected access experience.
- Click the ‘Login’ button.
- Authenticate on the Microsoft sign-in page.
- Choose the required method to load target Microsoft 365 mailboxes. If the automatic mailbox list does not return every required target, use the supported CSV-loading option and verify the destination mailbox list before continuing.
- Click the ‘Next’ button to continue
- Click the ‘Add New Connection’ button to create a new connection to your target Office 365 server. To use an existing connection, simply select it from the list and click ‘Connect to Existing’ to continue.
Step 4: T-online email to Microsoft 365 mailboxes mapping
- Select the required mapping option
- Where supported and selected, EdbMails can assist with target mailbox creation and automatic mapping. Verify Microsoft 365 licensing and review every source-to-target mailbox mapping before starting the production migration.
- Select the required mapping option
Step 5: Start T-Online email to Office 365 migration
- After mapping the mailboxes, click the ‘Start Migration’ button to initiate the migration process
- You can now track the migration progress using the progress bar. When the migration is complete, EdbMails will display a confirmation message.
- Click the 'View Logs' button to open the migration report, which provides a detailed summary of the entire process, including the total number of items migrated from each folder.
- After mapping the mailboxes, click the ‘Start Migration’ button to initiate the migration process
T-online email to Microsoft 365 Post-migration Tasks
- Verify the Microsoft 365 target
Review migration reports and check representative folders, messages, attachments, item counts, and user access.
- Update mail DNS when ready
If Microsoft 365 becomes the production mail service, update the required MX/DNS records only after target validation.
- Validate Outlook/client access
Confirm Microsoft 365 sign-in and Autodiscover behavior and recreate Outlook profiles only where required.
- Retain the source during validation
Keep the T-Online/Telekom mailbox available for the agreed transition period before decommissioning the old email service.
- Verify the Microsoft 365 target
Troubleshooting Guide for T-online email to Office 365 Migration
For troubleshooting, check out our knowledge base articles. If you have additional questions, browse the FAQs or engage with our customer care team for personalized assistance.
Benefits of EdbMails for T-Online to Office 365 Email Migration
- Provider-specific source connection
Use Telekom's documented secure IMAP endpoint and email-program password instead of generic server settings.
- Bulk mailbox migration
Load multiple T-Online mailboxes through CSV and process migration batches efficiently.
- Selective migration
Choose required mailboxes/folders and use supported IMAP filters.
- Incremental follow-up runs
Process eligible new or changed email items after the initial pass for staged cutover.
- Mailbox mapping and reports
Review source-to-target mapping and migration reports before changing production mail flow.
