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:

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
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

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.

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