Send email from .NET over SMTP

System.Net.Mail.SmtpClient is obsolete. Use MailKit, STARTTLS on 587, username `unitpost`, API key as password.

1. 1

   Add MailKit

   Shell

   dotnet add package MailKit

2. 2

   Send

   C#

   using MailKit.Net.Smtp;
   using MailKit.Security;
   using MimeKit;
   
   var message = new MimeMessage();
   message.From.Add(MailboxAddress.Parse("you@yourdomain.com"));
   message.To.Add(MailboxAddress.Parse("customer@example.com"));
   message.Subject = "Hello from .NET";
   message.Body = new TextPart("html") { Text = "<p>Sent via SMTP.</p>" };
   
   using var client = new SmtpClient();
   await client.ConnectAsync("smtp.unitpost.com", 587, SecureSocketOptions.StartTls);
   await client.AuthenticateAsync("unitpost", Environment.GetEnvironmentVariable("UNITPOST_API_KEY"));
   await client.SendAsync(message);
   await client.DisconnectAsync(true);

3. 3

   Verify delivery

   Confirm in Activity.