Sometime system generated emails get spammed or rejected by the mail servers due to configuration issues in the server that generated the email.
As a web developer/system administrator/ Application developer it's your duty to check the Spammyness of your Emails and keep the users happy.
www.mail-tester.com site give you the way to test your email easily and give you suggestions how to improve your ranking.
Only thing you need to do is go to the mail-tester.com site and it will generate a random email address account that you need to send your test email to. Once you send a test email to that account and click on the "Check your score" it will validate your email and let you know what issues you have in your system generated email.
Following are the 5 different images given depending on the ranking.
So next time when users complain that they are not receiving any system generated emails, mail-tester.com is the best way to solve the mystery.
Visit :- https://www.mail-tester.com/