Back to catalog
Mailcow
GPL-3.0Mailcow replaces hosted email like Fastmail with a self-hosted Docker suite featuring Postfix, Dovecot, SOGo webmail, and automated TLS management.
Open-source alternative to — compare it against:
Overview
Mailcow orchestrates a full-featured mail server stack using Docker Compose, linking Postfix, Dovecot, Rspamd, and SOGo through an internal network with an embedded Unbound DNS resolver. This architecture isolates mail routing, webmail, and spam filtering into separate containers while maintaining a unified REST API. It gives infrastructure teams complete control over mail storage and delivery pipelines without configuring bare-metal MTAs from scratch.
Why Mailcow instead of Fastmail
Hosting Mailcow places SMTP and IMAP daemons adjacent to your internal services, CI runners, and application backends. While Fastmail routes messages over public networks and enforces strict per-minute rate limits on outbound SMTP, Mailcow processes local mail at network speed without API quotas. An embedded Unbound DNS resolver prevents upstream lookup latency and avoids public DNSBL blocks, while Redis caches spam-filtering tokens and user sessions in memory.
The performance trade-off centers on host resources. Fastmail offloads all compute, memory, and spam scoring to managed infrastructure with sub-second sync. In contrast, Mailcow requires 4 GB to 6 GB of RAM, largely consumed by the ClamAV antivirus engine and Dovecot indexing processes. Running at scale requires allocating NVMe storage and tuning MariaDB connection pools to avoid I/O bottlenecks during mailbox synchronization.
What it does well
- Containerized service isolation: Runs Postfix, Dovecot, Rspamd, ClamAV, and SOGo in dedicated containers linked by internal networks, preventing configuration drift.
- Integrated REST API: Exposes endpoints to provision domains, mailboxes, and rate limits programmatically, enabling automated onboarding via CI/CD.
- Embedded recursive resolver: Bundles an Unbound container that queries root DNS servers directly, avoiding public resolver limits that degrade spam checks.
- Automated TLS and DKIM: Automatically provisions Let's Encrypt certificates via ACME and signs outbound messages with DKIM, SPF, and ARC in Rspamd.
- Groupware and mobile sync: Integrates SOGo for webmail, CalDAV calendars, CardDAV address books, and Microsoft ActiveSync support.
