In this article I will explain with an example, how to resolve the following error while sending email using MailKit library in .Net.
MailKit.Net.Smtp.SmtpCommandException: No such user here
Note: For more details on how to send Email using MailKit, please refer my article Send Email using MailKit in ASP.Net WebForms.
The following error occurs when you try to send email with MailKit using credentials in your .Net application.
<> No such user here
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: MailKit.Net.Smtp.SmtpCommandException: <> No such user here
.Net MailKit Error: No such user here
This error means that the Email Address (Username) supplied does not exist on the SMTP Server and hence it is rejected by the Server.