log4net: A Logging Library That's Been Quietly Doing Its Job Since 2007
You've probably inherited a .NET codebase at some point and found log4net already sitting in it, logging away, and you didn't think much about it. That's kind of the point. Apache log4net is one of those libraries that just works, and it's been working since it graduated from the Apache Incubator back in February 2007.
What It Does
Apache log4net is a logging library for .NET, and it's a subproject of the Apache Logging Services project. If you've worked with logging in the Java world, you'll recognize the lineage—log4net is the .NET counterpart to log4j, sharing the same conceptual approach to how you configure and route log messages.
The library targets net462 and netstandard2.0, which means it covers both legacy .NET Framework applications and modern .NET projects. That dual targeting is worth noting—it's not often you find a library that's equally comfortable in a decade-old enterprise app and a newer cross-platform project.
There's also an extension package worth knowing about: log4net.Ext.Mail. It's a MailKit-based SMTP appender for sending log events via email, and the README explicitly calls it the recommended replacement for the deprecated SmtpAppender. If you're still using the old SMTP appender, that's your migration path.
Why It's Cool
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It's boring in the best way. Logging libraries aren't supposed to be exciting. They're supposed to be reliable, predictable, and out of your way. log4net has had nearly two decades of production use across countless applications, and that track record matters more than any feature list.
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The Apache pedigree is real. This isn't a side project that someone abandoned. It's part of the Apache Logging Services project, with a mailing list, a proper contribution process, and the governance structure that comes with Apache. For teams that need to justify dependencies to a security or legal review, that backing carries weight.
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Dual targeting keeps you covered. Supporting both net462 and netstandard2.0 means you don't have to make a hard choice between maintaining legacy code and adopting modern tooling. You can use the same logging library in both, which simplifies things when you're gradually modernizing a codebase.
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The extension ecosystem addresses real gaps. The log4net.Ext.Mail package is a good example—rather than leaving users stranded on a deprecated appender, there's a maintained alternative built on MailKit. That's a small thing, but it signals the project is still being looked after.
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Documentation lives where you'd expect. The project maintains its documentation on the Apache log4net website, which means you're not hunting through wiki pages or scattered blog posts to figure out how to configure an appender.
How to Try It
Getting started is straightforward since it's distributed as a NuGet package.
- Install the package:
dotnet add package log4net
- If you need email-based logging, add the extension too:
dotnet add package log4net.Ext.Mail
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Head over to the official documentation at http://logging.apache.org/log4net for configuration details. The website covers appenders, layouts, and the various ways you can wire up logging for your application.
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If you want to contribute or just follow along, development happens on GitHub at https://github.com/apache/logging-log4net and on the project's mailing list. The README notes that for bigger changes, you should join the mailing list and discuss them before diving in—and you'll need to sign a Contributor License Agreement for substantial contributions.
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If you're building from source or working on the project itself, there are dedicated docs for that: CONTRIBUTING.md, BUILDING.md, and RELEASING.md are all in the doc folder of the repository.
Final Thoughts
log4net isn't trying to win any awards for innovation, and that's fine. It's a mature, well-maintained logging library with Apache backing, broad framework support, and a long history of being used in production. If you're starting a greenfield project, you might look at newer alternatives—but if you're working in an existing .NET codebase (especially one with legacy components), or you need something with a proven track record and proper governance, log4net remains a solid choice. The fact that it's still actively maintained and has addressed deprecated components with modern replacements suggests it's not going anywhere soon.
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