Stalwart v1.0: The Fastest Mail Server on the Planet

Stalwart v1.0 marks the first stable release of a Rust mail and collaboration server that began as an email-parsing library in 2021. The release prioritizes speed and long-term data stability: its database schema is now considered final, so future upgrades are intended to require installing a new version rather than disruptive data migrations. The developers describe months of profiling and optimization across more than 1,300 files, while also adding full-text search for PDFs and office documents.

Much of the performance work targets parsing and storage. SIMD and SWAR techniques let the server scan many bytes at once; a rewritten mail parser is reported to outperform several established parsers, while a new encoding library substantially speeds Base64 and quoted-printable decoding. Protocol parsers and other components were similarly optimized. Database changes reduce round trips, compress stored objects, and tune each supported backend; a redesigned cache keeps account indexes in memory to speed common IMAP operations and searches. The rebuilt search engine stores word positions, enabling phrase searches and more focused mailbox queries. Together, these changes make v1.0 both a performance-focused release and a milestone intended to make future upgrades more predictable.