What is mailcow?
mailcow is an open-source, Docker-based suite for hosting business email and groupware. It combines mail delivery, mailbox access, spam filtering and webmail, but the organisation running it remains responsible for maintenance and recovery. Its components include:
- Postfix for mail transfer
- Dovecot for IMAP/POP3
- Rspamd for spam filtering
- SOGo for webmail and groupware features
- ACME/Let’s Encrypt for SSL automation
- A modern UI for administration
The open-source software is only part of the cost. Budget for hosting, administration, updates, backups, monitoring and support, and test whether its features meet your users’ requirements.
Compare mailcow with supported Exchange options
| Feature | Microsoft Exchange On-Premise | Mailcow |
|---|---|---|
| Licensing Costs | Commercial licensing; check the chosen edition | Free, open-source |
| Hosting Control | Self-managed servers, on-premises or on hosted infrastructure | Self-managed servers, on-premises or on hosted infrastructure |
| User Interface | Enterprise-grade | Modern, intuitive |
| Email & Calendar Sync | Native Outlook support | SOGo and ActiveSync; test each required client and feature |
| Maintenance & Updates | Microsoft supplies updates; the operator installs and manages them | Project supplies updates; the operator installs and manages them |
| Spam Filtering | Protection depends on deployment and configured filtering | Rspamd filtering; configure and monitor it |
| Security | Built-in enterprise tools | Transport TLS and email authentication; not automatic end-to-end encryption |
Hosting control does not guarantee GDPR compliance
Self-hosting gives you a choice of hosting location and administration arrangements. That choice should be assessed alongside access controls, supplier agreements, retention, auditability and tested recovery.
mailcow does not make a deployment GDPR-compliant by itself. The organisation must assess its processing purposes, legal basis, security measures and processor arrangements. Encryption in transit also does not mean that message contents are end-to-end encrypted.
Test migration and client compatibility before switching
Use the official mailcow documentation to plan installation and migration. Test a representative mailbox, including calendars, contacts, shared access and mobile devices. Tasks to assess include:
- Migrating mailbox messages; IMAP alone does not migrate every Exchange feature
- Testing calendar, contact and mobile synchronisation for the chosen clients
- Verifying supported identity integrations and access controls
Document rollback, DNS changes and restore tests before moving production mail. Keep an owner for patching and monitoring after migration.
Exchange remains an on-premises option
Exchange Server 2016 and 2019 reached their published support end on 14 October 2025. This did not end all on-premises Exchange: Microsoft also offers Exchange Server Subscription Edition. Check the official Exchange Subscription Edition guidance and the lifecycle for your specific release.
Choose between mailcow, supported Exchange and a hosted service by comparing operational responsibility, client compatibility, recovery requirements and total cost, not licence cost alone.
mailcow is not a drop-in replacement for every Exchange workload. Test Outlook behaviour, shared mailboxes, calendars and applications that rely on Exchange-specific interfaces before deciding.
Review your existing mail platform through Cloud & Infrastructure and your user requirements through Managed IT Support. Discuss your email migration with an engineer before selecting a replacement.
