SMTP
Also known as: Simple Mail Transfer Protocol
Simple Mail Transfer Protocol (SMTP) is a standard by which e-mail is sent over the Internet.
The sender of an outgoing e-mail message offers this message to his provider's SMTP server. This SMTP server ensures that the message is delivered to the correct server elsewhere on the Internet. That location is determined from the DNS data of the recipient's domain name. The mail is then available to the recipient here through protocols such as POP3 and IMAP.
Security
To combat the sending of spam via the SMTP protocol, many providers use port blocking to make it impossible for customers to set up their own (open relay) SMTP server. This also often enforces the use of the respective ISP's own SMTP server.
Some providers choose to secure the use of the SMTP server with a username and password. These credentials usually correspond to incoming e-mail login credentials.
