Why can SmtpClient.SendAsync only be called once?

Question

I\'m trying to write a notification service (for completely legit non-spam purposes) in .NET using SmtpClient. Initially I just looped through each message and sent it, however

Answer 1

According to the documentation:

After calling SendAsync, you must wait for the e-mail transmission to complete before attempting to send another e-mail message using Send or SendAsync.

So to send multiple mails at the same time you need multiple SmtpClient instances.