These are websites on the Net that allow one to send email in which your IP address is not passed in the message header and your identity will remain hidden that even the email recipient will never know who exactly sent that message and from where.
It is not good to send death threats, abuse, slander or anything illegal to others.
Spamming to promote your service is also not a good culture.
The purpose of these service is perfect most probably for the following:
-catch a cheating spouse husband or wife.
-find out if your friend is are real friend
-give warnings to people
-inform the police about illegal activities
-inform the tax office about tax cheaters
-confess your love to somebody
-play an email joke with your friends
-when your own email service doesn’t work
-if your private email is banned by the recipient
-report fraud to your boss or institution
and many more reasons…