OpenMSP
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MIMEDefang

Email Security

Open Source
Free Tier
Self-hosted
OpenMSP Score
27
6
Reddit Impact Score
Github Score
41K
31Stars
8Forks
665Commits
GNU General Public License v2.0License
Jul 3, 2026Last commit

Alternative Vendors

Rspamd
Rspamd
SpamAssassin
SpamAssassin
Piler
Piler
MailScanner
MailScanner

Commercial Alternatives

Barracuda Email Security
Barracuda Email Security
Mimecast Email Security
Mimecast Email Security
Proofpoint Essentials
Proofpoint Essentials
Open source email filtering framework for scanning and modifying emails More detailed information about this vendor will be added soon.
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Key Features

Perl-Based Filtering Policies

Express filtering policies in Perl rather than C, making it quick and easy to write high-performance mail filters with the flexibility of a full programming language.

Sendmail Milter Integration

Uses Sendmail's Milter API to participate in SMTP connections, scanning messages once per message rather than per recipient for CPU efficiency.

Virus and Spam Filtering

Supports integration with SpamAssassin for spam detection and various antivirus scanners including ClamAV, with automatic detection of installed scanners.

MIME Message Manipulation

Can delete attachments, convert file formats (e.g., Word to HTML), replace attachments with URLs, add disclaimers, and implement sophisticated access controls.

Pros and Cons

Pros

Complete Open Source Freedom

GPL-licensed framework with full source code access, no licensing costs, and complete control over customization and deployment.

High Performance Architecture

Scans messages once per message rather than per recipient, making it more CPU-friendly than procmail-based systems with multiplexed processing.

Mature and Stable Platform

In use since 2000 with thousands of installations worldwide, proven stability and reliability in production environments.

Highly Flexible and Customizable

Perl-based filtering allows for sophisticated custom policies, integrations with multiple tools, and complete control over mail processing logic.

Cons

Sendmail Dependency

Requires Sendmail as the MTA and is not compatible with other mail transport agents, limiting deployment options for organizations using different MTAs.

Technical Complexity

Requires significant technical expertise in Perl programming, Sendmail configuration, and system administration for proper implementation and maintenance.

Community-Only Support

Technical support primarily provided through mailing lists and community forums, no commercial support option available for critical business needs.

Mail Message Modification

Potentially alters email message bodies, breaking the mail transfer agent convention of not modifying messages, which may cause compatibility issues.

Feature Comparison

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Frequently Asked Questions

Getting Started

OpenMSP is The MSP Knowledge Hub & Community Platform designed specifically for Managed Service Providers seeking to optimize their technology stack, reduce vendor costs, and discover open-source alternatives. We combine a comprehensive vendor directory, open-source solution catalog, and integrated community discussions to help MSPs make informed decisions.
Yes, completely free. Browse vendors and tools, read comparisons, and join community discussions - no cost, no registration required. OpenMSP is community-supported and focused on empowering MSPs to reduce costs and improve operational efficiency through open-source technology.
We help MSPs identify cost-effective alternatives to expensive commercial solutions, provide transparent vendor information, and connect you with proven open-source alternatives. Our platform enables MSPs to make informed decisions about their technology investments.
No account required for browsing vendors, reading comparisons, or accessing community content. Creating a free account with SSO (Microsoft, Google, or Slack) allows you to participate in discussions and save your favorite tools.

Platform Information

OpenMSP is currently community-supported. We focus on providing value to the MSP community first. Any future monetization will keep the core platform free for MSPs while maintaining our independence and commitment to unbiased information.
We focus exclusively on MSP needs with transparent vendor information and open-source alternatives. No vendor partnerships or sponsored listings - just honest, community-driven information to help MSPs make better technology decisions. Our biggest value is our community where MSPs help each other with questions, setup guidance, and sharing real-world experiences.
Our community of MSP professionals helps verify and update information. We also maintain direct research on tools and vendors to ensure accuracy. Community members can report outdated information, and we work to keep everything current.
OpenMSP was founded by Michael Assraf, who has extensive experience in the MSP industry and product leadership. As the former CEO & Founder of Vicarius, Michael grew a startup from $0 to $9M ARR with 500+ customers and deep experience working with MSPs, partners, and fundraising. OpenMSP represents his commitment to empowering the MSP community through better technology decisions and cost optimization.

Open-Source Tools & Alternatives

We assess tools based on active development, community size, documentation quality, production deployments by MSPs, and available support options. Tools must meet strict criteria for reliability and enterprise readiness.
Many open-source projects offer multiple support options including community forums, commercial support from vendors, professional services, and our community discussions where experienced MSPs share implementation guidance.