What changed
Stalwart released v1.0 on October 26, 2026, its first stable mail/collaboration server release after five years. The Rust-based server supports SMTP, IMAP, POP3, JMAP, CalDAV, CardDAV and WebDAV. Version 1.0 finalises the on-disk database layout, substantially rewrites MIME parsing and storage/search paths, adds full-text search inside document attachments and expands authentication controls. Its maintainers publish benchmark scripts and report winning 35 of 38 comparisons against a configured Postfix 3.11 and Dovecot 2.4 stack, but those results remain vendor-run. Crucially, v1.0 cannot directly open pre-1.0 data stores: v0.16 operators must first reach 0.16.27 and run stalwart-migrate; older versions can use a migration proxy and Vandelay. Clusters now require Redis coordination.
Why it matters
For a small team operating its own mail, the difference between routine binary updates and mandatory database conversion determines downtime, rollback planning and data-integrity risk. The stabilised schema could reduce future upgrade complexity, but getting to 1.0 requires a tested migration. Performance claims are unusually well documented with reproducible benchmark configurations, yet remain maintainer measurements rather than independent proof that Stalwart is universally faster. Teams evaluating a move from Postfix/Dovecot also need to consider operational maturity, mail deliverability, security, client compatibility and support boundaries.
Stable storage is the practical milestone
The 1.0 database schema is intentionally finalised so later releases can upgrade in place rather than repeating disruptive migrations. This release itself is a breaking storage transition: the new server will not open an old store. The official migration tool reads the old store, copies data to a new one, supports incremental reruns and preserves IMAP UIDs and change history. The final cutover still needs planning; OAuth users must sign in again and search indexes rebuild.
How existing installations move
For v0.16 installations, update to 0.16.27, back up and test, then use stalwart-migrate with a new empty v1.0 store. For v0.15 or earlier and gradual moves, the documented migration proxy and Vandelay can route accounts between old and new servers. Clusters must now use a Redis-family in-memory coordinator; single-node installations can use a built-in local store. Configuration keys were also renamed or restructured.
Performance and search changes are substantial but vendor-measured
The maintainers rewrote mail-parser using SIMD/SWAR, tuned RocksDB, PostgreSQL, MySQL, FoundationDB and SQLite backends, and redesigned mailbox caches. A new full-text index supports phrase searches and text extraction from PDF, Office, OpenDocument, EPUB and RTF attachments. On matched Azure servers, Stalwart says it won 35 of 38 head-to-head Postfix/Dovecot tests. Benchmark scripts and raw data are published, but independent reproduction and comparisons across different production configurations are still needed.
Security, protocols and integration caveats
The release includes JMAP object metadata, IMAP METADATA, more OAuth/OIDC controls and post-quantum DKIM2 support. Early community upgrade reports noted a Bulwark Native OAuth client ID issue, with a webmail fix published and native update expected. Administrators should test every mail client, authentication flow and relay before switching production. Enterprise-only AI spam classification should not be presented as a Community-edition feature.