btcpayserver/BTCPayServer/Services/Mails/EmailSender.cs

using Hangfire;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Mail;
using System.Threading.Tasks;

namespace BTCPayServer.Services.Mails
{
	// This class is used by the application to send email for account confirmation and password reset.
	// For more details see https://go.microsoft.com/fwlink/?LinkID=532713
	public class EmailSender : IEmailSender
	{
		IBackgroundJobClient _JobClient;
		SettingsRepository _Repository;
		public EmailSender(IBackgroundJobClient jobClient, SettingsRepository repository)
		{
			if(jobClient == null)
				throw new ArgumentNullException(nameof(jobClient));
			_JobClient = jobClient;
			_Repository = repository;
		}
		public Task SendEmailAsync(string email, string subject, string message)
		{
			_JobClient.Schedule(() => SendMailCore(email, subject, message), TimeSpan.Zero);
			return Task.CompletedTask;
		}

		public async Task SendMailCore(string email, string subject, string message)
		{
			var settings = await _Repository.GetSettingAsync<EmailSettings>();
			if(settings == null)
				throw new InvalidOperationException("Email settings not configured");
			var smtp = settings.CreateSmtpClient();
			MailMessage mail = new MailMessage(settings.From, email, subject, message);
			mail.IsBodyHtml = true;
			await smtp.SendMailAsync(mail);
		}
	}
}