The electronic mail service on the Internet is based on the Simple Mail Transfer Protocol (SMTP), which is defined in RFC 5321. 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. Mail servers which handle the electronic mail service on the basis of the SMTP protocol are also called SMTP servers.
The SMTP server used by the interNet Services in BS2000 is the product Postfix Version 3.6.15. This version applies for the creation time of this manual. Rebasing to a newer version can take place in the context of correction packages. This Open Source SMTP server created by Wietse Venema is characterized in particular by high performance, simple manageabilty, and a high degree of security. In addition, the partial compatibility of Postfix to the SendmailTM program contained in the interNet Value Edition guarantees simple migration from Sendmail to Postfix. Further details on this are provided in the section “Migration from Sendmail to Postfix”.
The following protocols are used by the Mail User Agents to access mailboxes on a remote server:
Internet Mail Access Protocol (IMAP, RFC 2060 etc.)
Post Office Protocol Version 3 (POP3, RFC 1939)
The IMAP and POP3 servers supplied with interNet Services support support the IPv6 and TLS protocols (see "TLS/SSL protection of IMAP/POP3 and SMTP connections").
To permit e-mails to be sent from BS2000, the interNet Services delivery package contains a simple User Agent, the Mail Sender (see the interNetServices User Guide). To permit automatic processing of received e-mails, interNet Services contains a Mail Reader on an IMAP/POP3 basis. If POSIX-SH is installed, POSIX also contains a simple, local User Agent (Mailx) for sending and processing text messages in BS2000.