POP before SMTP

SMTP - after-POP or POP-before - SMTP is a method to restrict the sending of e- mails in which the Simple Mail Transfer Protocol (SMTP) from the Post Office Protocol ( POP) is made dependent, which, though only for downloading e -mail is used, but allows the authentication.

Authentication for sending e -mails was not foreseen and long controversial, but was ultimately accepted because of spam and led to SMTP Auth.

When older SMTP - after-POP a mail server accepts e- mails only if carried out by the sending IP address from above within a certain time window, a retrieval of e- mails via POP, Login and Logout. Usually, such restrictions are limited to dynamic IP addresses on the Internet. Since due to network address translation to a specific user is no inference from one IP address possible, this method provides only an indication that a particular user is actually active.