Migrating email in a crisis
How to organise an emergency email migration when the supplier lets you down or the infrastructure gives way.
When email becomes an emergency
Email is a company’s first critical tool. When it goes down, the business stops. The most frequent crisis scenarios:
- The long-standing supplier cuts off the service (a dispute, bankruptcy, an unanticipated end of contract)
- The email service hosted on your premises is compromised by ransomware
- The hosting provider suffers a prolonged outage with no clear restoration date
- Mailboxes are saturated on shared hosting that can no longer take the load
The first few hours: stabilise
Before migrating, you need to restore a minimum flow of email.
1. Set up a temporary mail service
Create accounts on a reliable service (Google Workspace, a sovereign email service or a sovereign hosting provider if need be) for the critical addresses: management, sales, support.
2. Change the MX DNS records
Point the MX records (the DNS records for email) at the new service. Propagation takes between 1 and 24 hours. During that time, emails arrive on both systems.
3. Communicate internally
Warn the teams about the switchover. Give them the temporary credentials. Do not wait until everything is perfect before telling people.
Migrating the data
Once the flow is restored, recover the history.
- IMAP (the email synchronisation protocol): if the old server is still reachable, synchronise the mailboxes using an IMAP client or a tool such as
imapsync - PST/MBOX export: if local backups exist (PST from a desktop client, Thunderbird MBOX), import them into the new system
- Supplier backups: demand that your data be returned. It is a right, even in a dispute
# Example with imapsync
imapsync \
--host1 ancien-serveur.com --user1 user@domaine.fr --password1 "xxx" \
--host2 imap.nouveau-service.com --user2 user@domaine.fr --password2 "yyy"Mistakes not to make
- Changing the MX records without warning anyone: critical emails will be lost during the transition
- Forgetting aliases and mailing lists: recreate them on the new service before the switchover
- Neglecting SPF, DKIM and DMARC (the email authentication protocols): without those DNS records, your emails will end up in spam
- Not documenting: note every action, every record changed, so that you can roll back
After the crisis: do not repeat it
An emergency migration exposes your weaknesses. Once things are stable:
- Put in place an off-site backup of your email, for example via a Synology NAS (network-attached storage server) with MailPlus or an IMAP synchronisation tool that copies the mailboxes automatically. A NAS on site or hosted lets you keep a local copy that is independent of your email supplier.
- Document the full DNS configuration
- Make sure the contract with the new supplier includes a reversibility clause
- Test a switchover scenario once a year
Once things are stable, a digital maturity assessment or a partnership will keep you from living through the same crisis again.