How to add reference to legacy .NET assemblies?

Hello:
I'm using VS 2017 and I'm trying to use ASP .NET Core for building a REST API.

How would I reference a legacy .NET assembly in ASP .NET Core?

I referenced an existing assembly and when I try to create an instance in my Controller, it gives me this error below. Any help on this will be much appreciated.

An unhandled exception occurred while processing the request.

<div class="titleerror">FileNotFoundException: Could not load file or assembly 'SMTP.Net, Version=3.0.1.25, Culture=neutral, PublicKeyToken=986a9aa31056680b'. The system cannot find the file specified.</div>

WebApplication1.Controllers.TestController.Welcome(string name, int numTimes)

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• FileNotFoundException: Could not load file or assembly 'SMTP.Net, Version=3.0.1.25, Culture=neutral, PublicKeyToken=986a9aa31056680b'. The system cannot find the file specified.

  • WebApplication1.Controllers.TestController.Welcome

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