Migrating Email Boxes to a Host: The Lossless Method

Preparing the migration: Inbox inventory

Migrating emails starts with an inventory, not a transfer. List all the mailboxes to be moved, including their address, size, and contents: messages, contacts, calendars, and folders. Also note aliases, forwards, and distribution lists, which are often overlooked.

This inventory gives you the exact list of what must arrive intact on the new infrastructure. It is also the time to declutter: a migration is the opportunity to close unused mailboxes and archive what is no longer in use. A thorough inventory beforehand avoids discovering too late that a service mailbox was left behind. Also note who holds the administrative access to the old service: without it, you will be unable to export the mailboxes or confirm the switch when the time comes.

Choosing the method: IMAP, import, or transfer

There are three main methods. IMAP import copies messages from one mailbox to another by connecting simultaneously to both servers: it is the most common method, as it preserves the folder structure and messages. Export and re-import involves exporting mailboxes as files and then re-injecting them into the new server. Simple transfer only reroutes new messages: it does not move the history.

Choose based on the volume and source environment. For a small number of mailboxes, IMAP import is sufficient; for large volumes, a dedicated tool or hosting provider support is necessary. The important thing is to synchronize existing data before disconnecting the old service. Simple transfer can complement IMAP import by rerouting messages that arrive during the transition. Regardless of the method, verify that folders, subfolders, and labels are properly preserved, and not just received messages. A disorganized history afterwards costs more time to fix than the migration itself.

Create mailboxes before switching DNS

The order of operations is the key element of a lossless migration. First, create all mailboxes with the new hosting provider, using the same addresses. Then import the messages. Only after the mailboxes are created and synchronized should you modify the DNS zone.

This sequence ensures that no messages are rejected: the new mailbox already exists when delivery switches. If you modify the DNS first, messages sent to addresses that do not yet exist on the new server will bounce back to the sender. To create your mailboxes, follow our guide create and manage your email accounts.

Configure clients and mobile devices

Configure your devices on the new servers before the switch, in parallel with the old service. Retrieve the IMAP and SMTP settings from the new hosting provider, then enter them into your email software and mobile devices. Consult our guide to configure an IMAP account.

Testing the configuration in advance avoids the feared scenario: an effective switch without anyone being able to retrieve their emails due to unconfigured credentials. Each team member must have validated their connection on all their devices before Day J.

Switch MX records without downtime

MX records tell remote servers which host to route messages destined for your domain to. Switching them means redirecting delivery to the new hosting provider. This is the final step, not the first. The Simple Mail Transfer Protocol (SMTP) defines how messages are routed to the server designated by these records.

During the DNS propagation delay, some messages may still arrive on the old server. Keep it active for a few days and check it regularly, or set up a redirect, to avoid losing any late-arriving emails. For technical details, consult our guide modify MX records.

Verify after migration

After the switch, perform methodical checks: send a message to each mailbox and verify that it arrives, send a message from each mailbox to check delivery, then test replies and attachments. Also check aliases and forwards. Finally, verify authentication compliance: SPF, DKIM, and DMARC records must be operational on the new service.

A successful migration is validated by concrete tests, not just an estimate. Each mailbox deserves a test round-trip before considering the operation complete. Also test specific scenarios: sending a large attachment, replying to an old message, or accessing from a mobile network. It is often these cases that reveal previously unnoticed issues. Once mailboxes are migrated, monitor deliverability over time: consult our article why your emails end up in spam and, if you are also transferring your website hosting, our guide change hosting provider.

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Pitfalls to avoid

Common errors include switching MX records before creating accounts, overlooking aliases and forwards, neglecting contacts and calendars, or terminating the old service prematurely. Another pitfall is launching the switch on a Friday night without technical support available to intervene over the weekend: schedule the switch during business hours to allow for active monitoring.

In all cases, keep a complete backup of the old environment before any deletion. The migration must not destroy any data until the proper functioning of the new mailboxes has been validated: this essential precaution makes any incident reversible.

Staging for large teams

For an organization with many employees, proceed in batches: start with a pilot mailbox, validate the procedure, then progressively deploy on other accounts. This approach limits risks and allows you to adjust technical instructions before generalizing them. A large-scale migration is managed like an IT project, with a designated point of contact and a precise schedule.

FAQ

Can I migrate my old messages, or only new ones? Both. IMAP import or the synchronization tool copies existing history, while updating MX records redirects new flows. A complete migration plan addresses both aspects.

How long should I keep the old service after the switch? Keep it active for at least a few days, until DNS propagation is complete across all network resolvers, while continuing to check the old mailbox periodically.

Do contacts and calendars follow automatically? Not necessarily. The IMAP protocol only transfers emails and their folders. Depending on your source solution, contacts and calendars must be exported (often in vCard or iCalendar formats) and then manually re-imported or synchronized via dedicated protocols (CardDAV/CalDAV).