Mail overview

Please see this

Contents

- INDEX
- General Index
- Solaris
- Linux Index
- Other Unix types
- HP-UX Unix
- Unix Networking
- Unix Scripts
- Unix databases

Associated Information

- HTTP and SMTP troubleshooting

Useful Links

- UGU Networking Resorces

Electronic Mail Overview

There are three components to electronic mail:

MAIL USER AGENT - e.g. mailx, elm. dtmail, pine
MAIL TRANSFER AGENT - e.g. sendmail
MAIL DELIVERY AGENT - e.g. SMTP, local mailer, UUCP

MAILBOX - a file on a mail server to store mail, typically in /var/mail

MAIL HOST - main mail computer, mail is sent here when the other mail computer can't deliver it

MAIL SERVER - maintains mailboxes

CLIENT - receives mail, usuall no local /var/mail

The mail directory (e.g. /var/mail), can be NFS mounted if the mail server isn't the users local box. This saves having numerous mail servers.

Typical Local Mail Setup

Sendmail parses the message and using the rules in sendmail.cf, works out where to send it. It acts as an interface between mail user agent and mail transport agent, e.g. SMTP . It also supports forwarding mechanisms e.g. aliases, .forward file.

Remote Mailing

Mail is sent via the mail gateway. for mai sent over the internet, sendmail typically starts a SMTP session with the remote sendmail daemon. Usually, rather then deliver to the actual destination (which could be a PC over a modem line, probably not active), it delivers to the mail exchange server. During the transfer a DNS lookup is triggered. This finds the mail exchabge for the domain from the MX record (trying the one with the highest priority first). From there, the user can recover the mail using POP3 (which periodically and/or on demand, downloads the mail) or IMAP which lists the mail on the mail exchange.