Stalwart SMTP Server </h1>

Secure & Modern SMTP Server 🛡️

continuous integration License: AGPL v3 Documentation
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**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 authentication, strong transport security through DANE, MTA-STS and SMTP TLS reporting, and offers great flexibility and customization thanks to its dynamic configuration 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]( - **Milter** support for integration with external content filtering systems such as SpamAssassin and ClamAV. - Address rewriting. - Filtering, modification and removal of message parts or headers. - Inbound concurrency & rate limiting. - **Spam and Phishing** filter: - Comprehensive set of filtering **rules** on par with popular solutions. - Statistical **spam classifier** with automatic training capabilities. - DNS Blocklists (**DNSBLs**) checking of IP addresses, domains, and hashes. - Collaborative digest-based spam filtering with **Pyzor**. - **Phishing** protection against homographic URL attacks, sender spoofing and other techniques. - Trusted **reply** tracking to recognize and prioritize genuine e-mail replies. - Sender **reputation** monitoring by IP address, ASN, domain and email address. - **Greylisting** to temporarily defer unknown senders. - **Spam traps** to set up decoy email addresses that catch and analyze spam. - Flexible Queues: - Distributed and fault-tolerant queues. - Unlimited virtual queues with custom routing rules. - Delayed delivery with `FUTURERELEASE` and `DELIVERBY` extensions support. - Priority delivery with `MT-PRIORITY` extension support. - Outbound throttling & Disk quotas. - 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. - Redis, LDAP, PostgreSQL, MySQL, MSSQL and SQLite support. - Email aliases, mailing lists, subaddressing and catch-all addresses support. - Granular configuration rules. - REST API for management. - Memory safe (thanks to Rust). ## Get Started Install Stalwart SMTP Server on your server by following the instructions for your platform: - [Linux / MacOS]( - [Windows]( - [Docker]( All documentation is available at []( > **Note** > If you need a more comprehensive solution that includes IMAP and JMAP servers, you should consider installing the [Stalwart Mail Server]( instead. ## 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. ## Funding Part of the development of this project was funded through the [NGI0 Entrust Fund](, a fund established by [NLnet]( with financial support from the European Commission's [Next Generation Internet]( programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 101069594. If you find the project useful you can help by [becoming a sponsor]( Thank you! ## 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](/LICENSE) for more details. You can be released from the requirements of the AGPLv3 license by purchasing a commercial license. Please contact [email protected] for more details. ## Copyright Copyright (C) 2020-2023, Stalwart Labs Ltd.