Sending emails using SendGrid email provider and ASP.Net Core is very straightforward.
Firstly install SendGrid package through Package Manager Console using the following command

install-package SendGrid

Now create a account in Sendgrid.com and add an API key to use the SendGrid provider service.  Add this key to your AppSettings.Json or AppSettings.Development.Json under a new SendGridEmailSettings=>SendGridKey node.

AppSettings.Json:

{
"SendGridEmailSettings": {
"SendGridKey": <SendGrid Private API Key>
}
}

StartUp.cs:

public void ConfigureServices(IServiceCollection services)
{
……………………..
services.AddTransient<IEmailSender, EmailSender>();
services.Configure<AuthMessageSenderOptions>(options =>
Configuration.GetSection("SendGridEmailSettings").Bind(options));
}

EmailSender .cs

using Microsoft.AspNetCore.Identity.UI.Services;
using Microsoft.Extensions.Options;
using SendGrid;
using SendGrid.Helpers.Mail;
using System.Threading.Tasks;

public class AuthMessageSenderOptions
{
public string SendGridUser { get; set; }
public string SendGridKey { get; set; }
}
public class EmailSender : IEmailSender
{
public EmailSender(IOptions optionsAccessor)
{
Options = optionsAccessor.Value;
}
public AuthMessageSenderOptions Options { get; } //set only via Secret Manager
public Task SendEmailAsync(string email, string subject, string message)
{
return Execute(Options.SendGridKey, subject, message, email);
}
public Task Execute(string apiKey, string subject, string message, string email)
{
var sendGridClient = new SendGridClient(apiKey);
var sendGridMessage = new SendGridMessage()
{
From = new EmailAddress("ajitgoel@gmail.com", "Simpler Products-Social Media Scrubber"),
Subject = subject,
PlainTextContent = message,
HtmlContent = message
};
sendGridMessage.AddTo(new EmailAddress(email));
// Disable click tracking.See https://sendgrid.com/docs/User_Guide/Settings/tracking.html
sendGridMessage.SetClickTracking(false, false);
return sendGridClient.SendEmailAsync(sendGridMessage);
}
}

If you send an email and you do not receive it in your mailbox check the spam folder. My emails landed in the spam folder when I was testing the application.