I found it necessary to write this post because I have struggled with a "No Such User Here" error for sometime now when I configured a web application's SMTP Settings. PROBLEM: When I sent emails entering my SMTP details in the application, the mails would bounce with the message "No Such User Here" and an error code 550 or so. Searching on the internet I found no easy solution. DISCOVERY: Later, going through my hosting cpanel, I found that mail settings for my domain were set to "Local Mail Exchanger" even though I had changed the mx records to an external email provider. SOLUTION: Setting the mail exchanger option to "Automatically Detect Configuration" solved the problem.