What is the best way to test autoresponder emails?

What is the best way to test autoresponder emails?

Hi.  I am just finishing the development of my first autoresponder, which includes several emails (to be sent x days after sign-up).  I want to test the email (1) to ensure it is formatted properly and looks good on mobile and desktop clients, and (2) to ensure the autoresponder works as anticipated.

What is the best way to accomplish this testing?

Thank you.