Stalwart SMTP Server

Stalwart SMTP is a modern SMTP server developed in Rust with a focus on security, speed, and extensive configurability. It features built-in DMARC, DKIM, SPF and ARC support for message and sender authentication, strong transport security through DANE, MTA-STS, SMTP TLS reporting and offers great flexibility and customization thanks to its configurable rules and native support for Sieve scripts.

Key features:

• Sender and Message Authentication:
  • Domain-based Message Authentication, Reporting, and Conformance (DMARC) verification and failure/aggregate reporting.
  • DomainKeys Identified Mail (DKIM) verification, signing and failure reporting.
  • Sender Policy Framework (SPF) policy evaluation and failure reporting.
  • Authenticated Received Chain (ARC) verification and sealing.
  • Reverse IP (iprev) validation.
• Strong Transport Security:
  • DNS-Based Authentication of Named Entities (DANE) Transport Layer Security.
  • SMTP MTA Strict Transport Security (MTA-STS).
  • SMTP TLS Reporting (TLSRPT) delivery and analysis.
• Inbound Filtering and Throttling:
  • Sieve scripting language with support for all registered extensions.
  • Filtering, modification and removal of MIME parts or headers.
  • DNS block lists (DNSBL).
  • Greylisting.
  • Inbound concurrency and rate limiting.
  • Integration with external content filtering systems such as SpamAssassin and ClamAV.
• Flexible Queues:
  • Unlimited virtual queues.
  • Delayed delivery with FUTURERELEASE and DELIVERBY extensions support.
  • Priority delivery with MT-PRIORITY extension support.
  • Quotas.
  • Outbound throttling.
  • Custom routing rules.
• Logging and Reporting:
  • Detailed logging of SMTP transactions and events, including delivery attempts, errors, and policy violations.
  • Integration with OpenTelemetry to enable monitoring, tracing, and performance analysis of SMTP server operations.
  • Automatic analysis of incoming DMARC/TLS aggregate reports, DMARC/DKIM/SPF authentication failure reports as well as abuse reports.
• And more:
  • SASL authentication.
  • PostgreSQL, MySQL, MSSQL and SQLite support.
  • Granular configuration rules.
  • REST API for management.
  • Memory safe (thanks to Rust).

Get Started

Install Stalwart SMTP on your server by following the instructions for your platform:

• Linux / MacOS
• Windows
• Docker

You may also compile Stalwart SMTP from the source.

Support

If you are having problems running Stalwart SMTP, you found a bug or just have a question, do not hesitate to reach us on Github Discussions, Reddit or Discord. Additionally you may become a sponsor to obtain priority support from Stalwart Labs Ltd.

Documentation

Table of Contents

• Get Started
  • Linux / MacOS
  • Windows
  • Docker
• Configuration
  • Overview
  • General
  • Listeners
  • Rules
  • Scripting
  • Certificates
  • Remote
  • Databases
  • Lists
  • Resolver
  • Logging
• Inbound
  • Overview
  • Connect
  • Extensions
  • Ehlo
  • Authentication
  • Mail-From
  • Data
• Outbound
  • Overview
  • Schedule
  • Queue strategy
  • Throttling
  • Quotas
• Authentication
  • Overview
  • Signatures
  • DKIM
  • SPF
  • ARC
  • DMARC
  • IpRev
  • DNSBL
• Management
  • Overview
  • Configuration
  • Queue
  • Reports
• Development
  • Compiling
  • Tests
  • RFCs conformed

Roadmap

The following major features and enhancements are planned for Stalwart SMTP:

• Embedded Antispam and Antivirus
• WASM filters
• Distributed mode
• Web-based administration

Testing & Fuzzing

To run the test suite execute:

cargo test

To run the fuzz tests please refer to the Stalwart libraries that handle parsing for the SMTP server: smtp-proto, mail-parser, mail-auth and sieve-rs.

License

Licensed under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. See LICENSE for more details.

You can be released from the requirements of the AGPLv3 license by purchasing a commercial license. Please contact licensing@stalw.art for more details.

Copyright

Copyright (C) 2020-2023, Stalwart Labs Ltd.