6. Glossary

Alias

An alias is a way of forwarding an e-mail address to one or more new destinations.

Asterisk

Star-like symbol, ASCII code 42 decimal. Usually rendered six-pointed, but has also been spotted with five or eight points.

Bounce

Returned, undeliverable mail. Also the act of returning undeliverable mail. Bounces are returned to the sender address in the envelope* of the mail; the sender given in the header* is not used.

DNS

Dynamic|Distributed Name Server|System. A mechanism on internet to find addresses and other things associated with host names.

Envelope

Information about a mail message that is not in the header. This information is used by MTAs* to determine where mail must go, and if not deliverable, where it is to be returned. This information is typically transferred with commands of the SMTP* protocol.

ESMTP

Extended SMTP*. Has some more features.

Header

The initial part of a mail message, containing more or less meta information about the message; who sent it, what it is about, what it looks like, to whom you are to answer, etc. The structure and meaning is described in RFC* 822.

Mailbox

A destination where mails are sent to. It is more general than your in-box that contains the mails delivered to you. A mailbox can also be a program (which prints the mail to a printer) or other things.

Mail domain

The part after the @ of an email address. This is often called the "fully qualified host name", but with more modern mail transport (MX records), it's not really a host any more. So I prefer the term "domain".

Mailer

A "channel" for sendmail via which to output mails. This is a very general concept, including talking SMTP* or UUCP* to other mail servers, delivering a mail to a mailbox, piping a mail to a program; anything via which a mail can be sent ending up of sendmail's control.

Masquerade

Translate an address. This is the pure act of translation; it does not necessarily mean that the mail gets sent to another place. For redirecting e-mails there is aliasing*.

MTA

Mail Transfer Agent. A program that transfers mail from one place to another. Sendmail is an MTA.

MUA

Mail User Agent. A program that manages mail messages (on behalf of a user). Eudora, elm, pine, etc. are examples of MUAs.

Return Address

Place where to send the bounce* when an email turns out undeliverable. The return address is in the envelope* of the email. Some people know this as the "From " header*, since it often saved in mailboxes looking like a header line. It really isn't; it's part of the envelope.

RFC

Request For Comments. Documents written as proposal for a standard on the internet. They do not always make it to standard, but the ones about SMTP* (RFC 821) and mail message structure (RFC 822) did.

SMTP

Simple Mail Transfer Protocol. A commonly used protocol (language) used by MTAs* to exchange mail. Described in RFC* 821.

UUCP

Unix to Unix CoPy. A protocol used on many unix systems to transfer files between them. E-mail can also be transferred with this system.