This application is a clone of the homonymous application of the one developed by BrightSoul available at this link: https://github.com/BrightSoul/background-email-sender.
This project uses the MailKit package to deliver emails. The Hosted Service implements the IEmailSender interface from the Microsoft.AspNetCore.Identity.UI but you can make it implement some other similar interface if you don't want to depend upon ASP.NET Core Identity.
I thank Moreno G. for providing me with the appropriate information so that I could finish the implementation and make it usable for the production environment.
Edit the appsettings.json file with your SMTP server data. Then, just run the application by typing dotnet run. The .NET Core SDK 5.0 (or greater) must be installed in your system. Fill in the form and hit the Send button.