Sending and receiving electronic mail (e-mail) are among the most important services on the Internet. The role of post offices is taken over by mail servers, which are also called Mail Transfer Agents (MTA). Mail servers handle transfer of e-mails over the network and ensure they are delivered to mailboxes.
The electronic mail service on the Internet is based on the Simple Mail Transfer Protocol (SMTP), which is currently defined in RFC 5321. Mail servers that handle the electronic mail service on the basis of the SMTP protocol are also known as SMTP servers. Originally only pure text messages could be transferred, but today the MIME mechanism (Multipurpose Internet Mail Extensions, RFC 2045 through 2049) enables a wide range of formats (e.g. images) to be transmitted.
The SMTP server receives messages either from another SMTP server or from a Mail User Agent (MUA), the mail sender. The SMTP server can function as a mail relay or mail end system. The SMTP server uses the Domain Name Service (DNS) in order to select a suitable route to an end system.
The SMTP server used by the interNet Services in BS2000 is the product Postfix Version 3.9.0 (at the time the manual went to press), which has been ported to BS2000 and which is supporting IPv6 and TLS functionality. This Open Source SMTP Server created by Wietse Venema is characterized in particular by high performance, simple manageabilty and a high degree of security.