The best mail tester on the internet today is from Unlock The Inbox. They have an email configuration and authentication tester that is simple and easy to use.
All you have to do is send an email to:
Within 2 short minutes, they will reply back to the email you sent, showing you the results of 100's of different mail tests performed on your email. Their mail tester test for all the different RFC Standards, Postmaster Guidelines, and Best Practices.
About Mail Tester
Many mail testers on the internet today, only test with single focus, the mail tester that unlock the inbox provides, tests all the authentication standards with components from different providers. For instance if your mail test passes with GMAIL, it might not pass with HOTMAIL, even though standards should be the same, different providers implement those standards different.
The market leader mail tester
Unlock the Inbox has been testing mail since 2008 and has improved many ESP components through comparison testing of different email authentication providers. Having reported issues and providing test cases to major ESP they have quickly grown respected and is the go to source for mail testing.