Standard email clients usually behave differently with encrypted or signed emails.
This service creates a quantity of different test email and sends them to one particular receiver. You can test if your email client shows discrepancy in handling the different types and forms of emails. The authentication of the user is necessary in order to prevent misuse by sending massive amounts of emails.
For questions and comments you can reach us at firstname.lastname@example.org.
Link to the MailServlet: Demo MailServlet