For years, I have been using System.Net.Mail namespace to send email from my ASP.Net applications. Recently one of my friend asked my assistance in troubleshooting the email delivery issues from a newly deployed application. It was interesting that the same deployed code was sending email with the same configuration settings. However, I noticed, the test environment is Windows and the Production is Ubuntu. I wanted to understand is there any difference, do we need to add any extra parameters when using Linux, So I went into the SmtpClient documentation, that was used by the developer to send the Email.