Important, sending too many testing emails can block your IP address.
There is a protocol that is set in the server, linked with the mail functionalities that helps preventing unauthorised entry of the mails to the server. One of the principle acts as when too many test mails are sent from a server it considers it as a spam and it could harmful. When number of testing mails are sent from a IP. The IP gets blocked and blacklisted. Making the changes in the type of email can avoid these instance to happen.
So, you should test it ONLY few times.