The current NuGet package targets .NETCoreApp 2.1. My app is .NETCore 3.1. I'm getting warnings like:

Perhaps the library should target .NETStandard for better compatibility with more targets?

The Usenet server that I am using does not support the OVER command. It only supports the older XOVER command. For backwards compatibility, perhaps this library should also support XOVER. The syntax is identical to OVER, except for the additional X in XOVER.

I've already coded XOVER by copying OVER and adding the X. There is certainly a more elegant way to implement XOVER without copying the entire method. If this is something valuable to the project, I will create the more elegant solution and create a pull request.

Have you considered publishing this library as a Nuget package?

When there is a Usenet article with no body (that is, the entire message is the subject line only), the library crashes in OverAsync when processing the return from the server. Consider the "parts" for this article header:

When the number of lines ("parts[7]") is parsed into an int at line 624 of NttpClient.cs, an exception is thrown as string.Empty can not be parsed as an int value.

(I can submit a pull request to fix this issue.)

Ideally, a dependency shouldn't dictate to the application what logging library to use. As the library consumer, I should be able to tell the library what library my application uses (typically using Microsoft.Extensions.Logging). Doing so everything - the app and the library - uses a common logging infrastructure. With the dependency on log4net, I am required to install log4net when I deploy my app.