Networking overview

Distributed electronic mail

Electronic mail (e-mail) on the SCO OpenServer system is handled by two distinct processes:

The Mail User Agent (MUA) enables users to send, read, and manage mail messages, and transfers outgoing mail to a Mail Transfer Agent.
The Mail Transfer Agent (MTA) is the group of programs that route and deliver messages to their destinations.

On a stand-alone system, the MUA (such as mail) and MTA (such as sendmail) interact directly. The MUA, acting on behalf of the sending user, contacts the MTA, which routes the mail to the local recipient. The recipient reads the mail by using an MUA.

On a networked system, the MTA on the sending system has the additional task of determining whether the mail should be delivered to a local user or sent to another machine on the network, and, if sent to another machine, what communications channel (such as SMTP, the Simple Mail Transport Protocol) to use. When the MTA on the destination system receives the mail message, that MTA forwards the message to the appropriate user.

SCO OpenServer provides a choice of Mail Transfer Agents:

MMDF

(Multichannel Memorandum Distribution Facility), the SCO MTA that is included with the SCO OpenServer operating system

sendmail

a commonly used alternative MTA that is also included with the SCO OpenServer operating system

MMDF offers several substantial benefits over sendmail, including:

Configuration files that are easy to read and understand.
The ability for end users to configure their own sorting parameters.
A larger set of supported delivery agents.

For a more detailed comparison of the differences between MMDF and sendmail, see ``Comparison of sendmail with MMDF''. For more information on these MTAs, see ``Managing mail with MMDF'', and ``sendmail administration''.

Both MTAs can use a variety of hostname-to-Internet address mapping schemes; the most effective when connecting to the Internet is the Domain Name Service (DNS).

Configuring a mail transfer agent

To configure electronic mail, you must complete the following procedures:

configuring DNS (Domain Name Service) if desired.
choosing an MTA (Mail Transfer Agent), either at installation time or after the system is installed.
establishing physical connections and configuring networking drivers.
configuring the MTA.

Administering a mail transfer agent

Administering a mail system includes regularly:

monitoring the log file.
monitoring the mail queue.
modifying parameters.