Chapter 12 Mail Services (Overview)

Setting up and maintaining an electronic mail service involves complex tasks that are critical to the daily operation of your network. As a network administrator, you might need to expand an existing mail service. Alternately, you might need to set up a mail service on a new network or a subnet. The chapters on mail services can help you plan and set up a mail service for your network. This chapter provides links to descriptions of new features in sendmail, as well as a list of other sources of information. The chapter also provides overviews of the software and hardware components that are required to establish a mail service.

• What's New With Mail Services

• Other sendmail Information Sources

• Introduction to the Components of Mail Services

See Chapter 13, Mail Services (Tasks) for procedural information about how to set up and administer mail services. For details, refer to Task Map for Mail Services.

See Chapter 14, Mail Services (Reference) for a more detailed description of the components of mail services. This chapter also describes the mail service programs and files, the mail routing process, the interactions of sendmail with name services, and the features in version 8.13 of sendmail. See Changes in Version 8.13 of sendmail.

What's New With Mail Services

This section provides information about new features in various Solaris releases.

Changes in this Release

The following changes have been made in the Solaris 10 7/10 release release:

• The default version of sendmail has been updated to 8.14.

• The sendmail instance was split into two instances to provide better management of the traditional daemon (svc:/network/smtp:sendmail) and the client queue runner (svc:/network/smtp:sendmail-client).

• The system can be configured to automatically rebuild the sendmail.cf and the submit.mc configuration files. The required steps are documented in How to Automatically Rebuild a Configuration File.

• By default, the sendmail daemon runs in the new local daemon mode. The local–only mode only accepts incoming mail from the local host or loopback SMTP connections. For instance, mail from a cron job or between local users would be accepted. Outbound mail is routed as expected, only the incoming mail is changed. The -bl option is used to select the local-only mode, also known as the Become Local mode. For more information about this mode, see the sendmail(1M) man page. For instructions on how to change back to the -bd or Become Daemon mode, see How to Use sendmail in the Open Mode.

Changes in the Solaris 10 1/06 Release

Starting in the Solaris 10 1/06 release, sendmail supports SMTP using Transport Layer Security (TLS). For more information, see the following:

• Support for Running SMTP With TLS in Version 8.13 of sendmail

• How to Set SMTP to Use TLS

For a complete list of features in the Solaris 10 1/06 release, see Oracle Solaris 10 9/10 What’s New.

Changes in the Solaris 10 Release

Starting in the Solaris 10 release, sendmail version 8.13 is the default. For information about version 8.13 and other changes, see the following:

• Flags Used and Not Used to Compile sendmail

• MILTER, Mail Filter API for sendmail

• Versions of the Configuration File

• Enhancement for vacation Utility

• Contents of the /etc/mail/cf Directory

• Changes in Version 8.13 of sendmail

• Support for TCP Wrappers From Version 8.12 of sendmail

Additionally, the mail service is managed by the Service Management Facility. Administrative actions on this service, such as enabling, disabling, or restarting, can be performed by using the svcadm command. The service's status can be queried by using the svcs command. For more information about the Service Management Facility, see the smf(5) man page and Chapter 18, Managing Services (Overview), in System Administration Guide: Basic Administration.

Other sendmail Information Sources

The following is a list of additional information sources about sendmail.

• Costales, Bryan. sendmail, Third Edition. O'Reilly & Associates, Inc., 2002.

• Home page for sendmail – http://www.sendmail.org.

• FAQ for sendmail – http://www.sendmail.org/faq.

• README for new sendmail configuration files – http://www.sendmail.org/m4/readme.html.

• A guide for issues that are related to migrating to more recent versions of sendmail – http://www.sendmail.org/vendor/sun/.

Introduction to the Components of Mail Services

Many software and hardware components are required to establish a mail service. The following sections give a quick introduction to these components. These sections also provide some of the terms that are used to describe the components.

The first section, Overview of the Software Components, defines the terms that are used when discussing the software parts of the mail delivery system. The next section, Overview of the Hardware Components, focuses on the functions of the hardware systems in a mail configuration.

Overview of the Software Components

The following table introduces some of the software components of a mail system. Refer to Software Components for a complete description of all of the software components.

Overview of the Hardware Components

A mail configuration requires three elements, which you can combine on the same system or provide in separate systems.

• A mail host – A system that is configured to handle email addresses that are difficult to resolve

• A minimum of one mail server – A system that is configured to hold one or more mailboxes

• Mail clients – Systems that access mail from a mail server

If users are to communicate with networks outside your domain, you must also add a fourth element, a mail gateway.

Figure 12–1 shows a typical electronic mail configuration, using the three basic mail elements plus a mail gateway.

Figure 12–1 Typical Electronic Mail Configuration

Each element is described in detail in Hardware Components.