Which method is good for bulk mailing smtpServer.SendAsync() or smtpServer.Send()

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C#

Hi ,


I want to send bulk mails(more than 100/day).

When i am using smtpServer.SendAsync() method then i am getting an error :

System.Net.Mail.SmtpClient:An asynchronous call is already in progress 

At the same time i need STOP button where i can stop the mails being sending.

Anybody please help to me solve this problem.