Software Components

Each mail service includes at least one of each of the following software components.

• Mail User Agent

• Mail Transfer Agent

• Local Delivery Agent

This section also describes these software components.

• Mailers

• Mail Addresses

• Mailbox Files

• Mail Aliases

Mail User Agent

The mail user agent is the program that acts as the interface between the user and mail transfer agent. The sendmail program is a mail transfer agent. The Solaris operating environment supplies the following mail user agents.

• /usr/bin/mail

• /usr/bin/mailx

• $OPENWINHOME/bin/mailtool

• /usr/dt/bin/dtmail

Mail Transfer Agent

The mail transfer agent is responsible for the routing of mail messages and the resolution of mail addresses. This agent is also known as a mail transport agent. The transfer agent for the Solaris operating environment is sendmail. The transfer agent performs these functions.

• Accepts messages from the mail user agent

• Resolves destination addresses

• Selects a proper delivery agent to deliver the mail

• Receives incoming mail from other mail transfer agents

Local Delivery Agent

A local delivery agent is a program that implements a mail delivery protocol. The following local delivery agents are provided with the Solaris operating environment.

• The UUCP local delivery agent, which uses uux to deliver mail

• The local delivery agent, which is mail.local in the standard Solaris release

Chapter 24, What's New With Mail Services (Reference) provides information on these related topics.

• New Delivery Agent Flags

• New Equates for Delivery Agents

• Changes to mail.local

Mailers

Mailer is a sendmail-specific term. A mailer is used by sendmail to identify a specific instance of a customized local delivery agent or a customized mail transfer agent. You need to specify at least one mailer in your sendmail.cf file. For task information, refer to Building the sendmail.cf Configuration File (Task) in Chapter 22, Mail Services (Tasks). This section provides a brief description of two types of mailers.

• Simple Mail Transfer Protocol (SMTP) Mailers

• UNIX-to-UNIX Copy Program (UUCP) Mailers

For additional information about mailers, see http://www.sendmail.org/m4/readme.html or /usr/lib/mail/README.

Simple Mail Transfer Protocol (SMTP) Mailers

SMTP is the standard mail protocol that is used on the Internet. This protocol defines these mailers.

• smtp provides regular SMTP transfers to other servers

• esmtp provides extended SMTP transfers to other servers

• smtp8 provides SMTP transfers to other servers without converting 8-bit data to MIME

• dsmtp provides on-demand delivery by using the F=% mailer flag. Refer to Changes to the MAILER() Declaration and New Delivery Agent Flags in Chapter 24, What's New With Mail Services (Reference).