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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Anti-Spam SMTP Proxy Server (ASSP) is open-source mail-server software designed to sit between incoming SMTP connections and an existing mail server. It evaluates mail during SMTP handling, using configurable filtering and authentication-related checks; depending on configuration, messages may be rejected, tagged, or relayed onward. It is intended for administrators managing mail infrastructure, not as a consumer email app or hosted filtering service.
What ASSP does in a mail system
ASSP acts as an SMTP intermediary in front of a regular mail transport. An archived quick-start guide describes it as relaying the SMTP conversation to that server while applying configurable checks. In that guide, spam can be rejected immediately with a 5xx SMTP response or tagged and delivered, while accepted mail is handed to the regular server for further processing. These are documented behaviors, not a guarantee that every current installation uses those actions or defaults. SourceForge project listing
That position in the mail flow matters: ASSP is not itself a mailbox service. Administrators still need an underlying mail server, suitable DNS and network configuration, and a plan for monitoring and maintaining the proxy.
Filtering and mail-handling features
The project repository lists a broad set of filtering and control capabilities. These are project feature claims; they do not establish how a particular release is configured, how well a filter performs, or what detection rates an operator should expect. ASSP project repository
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#1 Best Overall
- SonicWall Comprehensive Anti-Spam Service for TZ270 - 2 Year License (02-SSC-6674)
- Advanced Spam & Phishing Filtering: Blocks unwanted emails, phishing attempts, and spoofed messages before they reach users.
- Real-Time IP Reputation & Cloud Lookups: Uses SonicWall’s threat intelligence network to identify and block known spammers and malicious domains.
- Integrated with SonicWall Appliances: Runs natively on SonicWall firewalls and Email Security appliances with no additional hardware required.
- Email Continuity & Clean-Up Tools: Reduces email server load and ensures clean, filtered mail delivery to help protect business productivity.
- Reputation and connection controls: weighted DNS-based block lists and URI lists, plus greylisting.
- Message analysis: regular-expression filtering, Bayesian analysis, and Hidden Markov Model analysis.
- Sender and domain checks: SPF and SRS support, along with DKIM checks and signing and DMARC.
- Content and malware controls: attachment blocking and integrations with ClamAV and FileScan.
- Other integrations and protections: LDAP and backscatter detection.
- Transport security: TLS is included in the listed capabilities.
Because these functions are configurable and depend on the surrounding mail setup, assess the exact build and configuration you plan to run rather than assuming every listed capability is enabled or effective by default.
Deployment routes documented by the project
The repository shows a Docker example, while the SourceForge listing advertises ready-to-run virtual appliances for specific operating-system versions. Neither source provides a complete, current compatibility matrix, so treat these as documented options rather than proof of universal platform support.
Rank #2
- SonicWall Comprehensive Anti-Spam Service for TZ270W - 1 Year License (02-SSC-6679)
- Advanced Spam & Phishing Filtering: Blocks unwanted emails, phishing attempts, and spoofed messages before they reach users.
- Real-Time IP Reputation & Cloud Lookups: Uses SonicWall’s threat intelligence network to identify and block known spammers and malicious domains.
- Integrated with SonicWall Appliances: Runs natively on SonicWall firewalls and Email Security appliances with no additional hardware required.
- Email Continuity & Clean-Up Tools: Reduces email server load and ensures clean, filtered mail delivery to help protect business productivity.
| Route | What the source documents | What to verify |
|---|---|---|
| Docker | The repository example exposes ports 25, 587, 465, 2525, and 55555, and retains ASSP data in a persistent volume. Its example also includes a MariaDB service. The page uses different image versions in separate examples. ASSP project repository | Confirm which ports your design actually needs, how the image is maintained, what data must persist, and whether the database is required for your chosen setup. The example is not a production security baseline. |
| Virtual appliance | SourceForge advertises appliances for Ubuntu 20.04 LTS and FreeBSD 12.2. SourceForge project listing | Confirm that the appliance is available and maintained for your intended use, and that its stated operating-system versions meet your environment’s support requirements. |
Operational checks before putting ASSP in front of mail
A public-facing SMTP proxy needs a host and network path that allow the mail traffic you intend to handle. Hosting is an infrastructure choice, not a service supplied by ASSP. Before deploying, check:
- SMTP access: Your host and firewall must allow the inbound and outbound SMTP ports required by your mail-flow design. Verify provider policies rather than assuming standard mail ports are open.
- Administration: Ensure you can manage the operating system or container, apply updates, inspect logs, and recover the service.
- Persistent state: For a container deployment, identify which application data must survive a restart or replacement and configure durable storage accordingly.
- Mail routing: Plan how accepted mail reaches the existing mail server and how rejected or tagged messages should be handled. Test the intended SMTP responses before directing production traffic.
- Security: Review the actual image or appliance configuration, credentials, exposed ports, and access controls. Do not copy example settings into production without review.
Version and license details need artifact-level verification
The available project pages do not establish one unambiguous authoritative current download. The SourceForge listing identifies version 2.8.1 build 24261 as its professional version and gives 2026-07-23 as its last-update date; the repository’s Docker examples refer to an older 2.6.5 image. These are statements from separate pages, not confirmation that either identifies the latest release for every distribution. SourceForge project listing ASSP project repository
Rank #3
- SonicWall Comprehensive Anti-Spam Service for TZ270 - 5 Year License (02-SSC-6677)
- Advanced Spam & Phishing Filtering: Blocks unwanted emails, phishing attempts, and spoofed messages before they reach users.
- Real-Time IP Reputation & Cloud Lookups: Uses SonicWall’s threat intelligence network to identify and block known spammers and malicious domains.
- Integrated with SonicWall Appliances: Runs natively on SonicWall firewalls and Email Security appliances with no additional hardware required.
- Email Continuity & Clean-Up Tools: Reduces email server load and ensures clean, filtered mail delivery to help protect business productivity.
The license labels also differ: GitHub displays GPL-3.0, while SourceForge displays GPLv2. Do not treat those labels as interchangeable or assume they settle the terms for a particular package. Inspect the license file bundled with the specific download or image you intend to deploy and obtain qualified advice if the distinction affects your use.
SourceForge also says development of version 1 stopped at the end of 2014 and encourages upgrading to V2. That is a warning against treating a V1 listing as current guidance; it does not by itself establish the maintenance status of every V2 artifact. SourceForge project listing
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Who should consider ASSP?
ASSP is most relevant to administrators who want a configurable SMTP filtering layer in front of an existing mail system and can operate the associated network and server components. It is a poor fit for someone seeking a turnkey hosted email service, or for an organization that cannot maintain a mail proxy and verify the release, settings, and license of its chosen build.
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