Migration to .NET 9
NoSpamProxy 16 is based on .NET 9, Microsoft’s development platform, for the first time. This has several practical implications for the operation and performance of NoSpamProxy Server.
.NET 9 is designed to be cross-platform, meaning that NoSpamProxy can generally be run on various operating systems without being tied to a specific version of Windows. This is a relevant factor for environments with heterogeneous infrastructure or long-term operational planning. Future deployments can thus be designed more flexibly; for example, the NoSpamProxy team is currently working on support for Linux systems.
In addition, Microsoft releases a new major version of the .NET Framework annually; NoSpamProxy will align with this cycle in the future, meaning the software will regularly remain up to date with the latest framework version. This reduces technical debt, simplifies long-term maintenance, and ensures that security updates for the framework can be incorporated promptly.
In addition, .NET 9 delivers measurable performance improvements over previous versions, for example in terms of speed and memory usage. For an email security solution that processes high volumes of messages in real time, this has a direct impact on stability and resource efficiency. The migration to .NET 9 thus represents a substantial modernization of the technical foundation upon which all other NoSpamProxy features are built.
Improved MIME Type Detection
NoSpamProxy Server 16 significantly enhances MIME type detection in the content filter. New MIME types and those that were previously difficult to detect are now identified more reliably. This provides greater transparency and security, and the more accurate analysis of file attachments supports the evaluation of incoming messages.
Note on existing configurations
Due to the more precise detection, it may be necessary to adjust existing settings in the content filter. In the past, some file types were classified less specifically. With the new detection, these are now assigned more accurately. As a result, existing filter rules may no longer function as intended.
An example: Previously, CSV files were often recognized as “text/plain,” but are now correctly classified as “text/csv.”
If your filter rules specifically target certain MIME types, we recommend reviewing them and adjusting them as necessary.
OpenTelemetry Integration
NoSpamProxy Server 16 now supports OpenTelemetry, the open and vendor-neutral standard for collecting telemetry data such as metrics, traces, and logs.
Specifically, this means that the path an email takes through the system can be tracked in greater detail. Where log analysis or manual diagnostics were previously necessary, traces can now be automatically captured and analyzed in a central monitoring system. This significantly simplifies troubleshooting and gives operators a clearer, more consistent view of ongoing operations—especially in larger environments where NoSpamProxy Server is operated as part of a broader IT infrastructure.
Since OpenTelemetry is a widely adopted standard, organizations that already operate a corresponding monitoring infrastructure benefit immediately from the integration. The choice of the specific monitoring backend remains completely flexible and independent of NoSpamProxy Server itself.
The introduction of OpenTelemetry will also be accompanied in the medium term by the phasing out of the existing Windows performance counters. These will be replaced by OpenTelemetry in one of the upcoming versions. The transition will be announced in a timely manner.
Reputation Filter: Reject with DMARC p=none
The reputation filter in NoSpamProxy Server 16 takes into account whether a sending domain has configured the DMARC policy p=none and now offers new action options.
DMARC is an email authentication standard that allows domains to specify how to handle unauthenticated messages. The p=none policy means that while DMARC is configured, no enforcement measures are applied, neither quarantine nor rejection. In this case, messages are delivered regardless of the authentication results. In practice, this configuration is often a sign of an incomplete or still-developing email setup on the sender’s side; however, it can also indicate domains that deliberately choose not to implement a stricter policy.
NoSpamProxy Server 16 now allows you to override the sender’s preference and reject the email if the DMARC check fails, even if p=none is specified. In doing so, the filter closes a gap that previously represented a common vulnerability in sender validation and enables more nuanced handling of incoming messages according to the recipient’s preferences and specifications.
Additional Changes
New System Requirement: SQL Server Express 2025
Starting with NoSpamProxy Server version 16, Microsoft SQL Server Express 2025 is required as the database backend. Older versions of SQL Server Express are no longer supported. Administrators who wish to use version 16 should check their database environment accordingly before migration and update it if necessary. We recommend planning this step well in advance to avoid delays when updating to NoSpamProxy Server 16.
TCP Proxy: Old version is being removed
NoSpamProxy Server 16 relies exclusively on the new TCP Proxy. The previous, older TCP Proxy is being removed with this version and is no longer available.
If the old TCP Proxy is still in use in your environment, migration to the new TCP Proxy is mandatory before the update. Systems that are still configured for the old proxy after the update will not function correctly. We therefore recommend including the migration to the new TCP Proxy in your update planning early on and completing it before the actual update to NoSpamProxy Server 16.
Notes and Announcements
Setup blockers have been implemented for the following system configurations:
- SQL Server versions older than 2016 Service Pack 1
- SQL Server Express versions older than 2025
Planned changes in upcoming versions:
- SQL Server Standard/Enterprise versions older than 2019 will be deprecated with the release of NoSpamProxy Server 16.2. Environments still running older SQL Server versions should plan for migration accordingly.
- Windows Server versions older than 2019 will be discontinued as of December 31, 2026. As of that date, NoSpamProxy Server will no longer be supported on older Windows Server versions.
- NTLM authentication will be replaced by Basic Authentication. Existing scripts that use NTLM will no longer work starting with NoSpamProxy Server 16.1 and must be adapted before updating to version 16.1.
- Performance counters will be replaced by OpenTelemetry in a future version. The exact date will be announced in due course.
You can find the new version of NoSpamProxy Server under Software Download.
An overview of all changes can be found in the Release Notes.
Download the new version now!
You can always find the latest versions of NoSpamProxy Server on our download page. Update now to enjoy maximum email security and the latest features.
