While SpamAssassin has been the go-to open-source spam filtering solution for decades, modern email infrastructures often need more performant and scalable alternatives. The Perl-based architecture shows limitations in high-volume environments, and its machine learning capabilities haven't kept pace with contemporary spam techniques.

rspamd emerges as a compelling replacement, offering:

• C++ core for better performance (processes 1000+ messages per second)
• Built-in Redis support for distributed processing
• Modern machine learning (including neural networks)
• Lua scripting for custom rules

Basic rspamd setup for Postfix:

# In /etc/rspamd/local.d/worker-proxy.inc
bind_socket = "localhost:11332";
milter = yes;
timeout = 120s;

Postfix integration:

# In /etc/postfix/main.cf
smtpd_milters = inet:localhost:11332
non_smtpd_milters = inet:localhost:11332

When moving from SpamAssassin to rspamd:

1. Convert custom rules using rspamadm configconvert
2. Preserve Bayes data via migration tools
3. Run both systems in parallel during transition

Example of custom Lua rule:

-- In /etc/rspamd/rules/myrules.lua
rspamd_config:register_symbol({
  name = 'MY_CUSTOM_RULE',
  score = 3.0,
  callback = function(task)
    local header = task:get_header('X-Special')
    return header and header:lower():find('promotion')
  end
})

The ecosystem also includes web UI, prometheus metrics, and integration with popular MTAs like Postfix, Exim, and Sendmail.

While SpamAssassin has been the go-to open-source spam filter for decades, modern email systems demand higher performance and scalability. Rspamd emerges as a compelling alternative with its:

• Multi-threaded architecture (handles 10x more messages/second)
• Native Redis support for distributed processing
• Lua-powered rule scripting (vs. SpamAssassin's Perl)
• Real-time statistical analysis with OSBF

# Sample rspamd configuration snippet showing modern features
rules {
    spamassassin {
        priority = 10;
        ruleset = "/etc/rspamd/sa-rules";
        # Process SA rules with enhanced performance
    }
    rbl {
        # Cloud-based RBL checks
        rspamd_providers = ["RSPAMD", "SURBL"];
    }
}

Beyond raw performance metrics, Rspamd offers developer-friendly features:

• RESTful HTTP API for integration (vs. SpamAssassin's pipe protocol)
• Native support for ARC authentication
• Machine learning with statistical module

Transitioning existing configurations is straightforward. Rspamd includes built-in compatibility for SpamAssassin rules:

# Convert SA rules to Rspamd format
rspamadm configwizard -s /etc/spamassassin -d /etc/rspamd/sa-compat

# Enable legacy support in rspamd.conf
composite "SA_RULES" {
    plugins = ["spamassassin"];
    expression = "DBL_SPAM || SA_RULES";
}

Tests on AWS c5.2xlarge instances show significant differences:

Rspamd's controller-worker architecture shines in clustered environments:

worker.controller {
    bind_socket = "*:11334";
    secure_ip = ["192.168.1.0/24"];
}

worker.normal {
    count = 4; # Number of worker processes
    task_timeout = 10s;
}