[Gllug] mutt & gpg revisited

[tet at accucard.com]

>I'm not very clear on the ins and outs of the whole mail subsystem,
>whether the MUA calls procmail before sending it on to the MTA or
>whether the MTA calls procmail internally but in theory it would seem
>plausible that procmail could process outgoing mail. I saw some
>reference on Google about this but it was a little unclear.

Basically, you have three types of program:

	MUA: mail user agent.
	MTA: mail transport agent. 
	MDA: mail delivery agent. 

The MUA is what the end user sees. Examples include mh, mutt, pine,
spruce, evolution, Outlook, etc. ad infiniitum.

The MTA is resposible for transferring mail between machines. Examples
include the ubiquitous sendmail, plus others such as exim, qmail etc.

The MDA is responsible for delivering mail to the end user once it's
reached its final destination. Under Unix, this typically involves just
sticking the message in the appropriate user's $MAIL file. Examples
include deliver, slocal and procmail. Procmail is the default MDA in
Red Hat and probably other distributions. With procmail as an MDA, the
user can specify different behaviour than appending to $MAIL by using
an appropriate .procmailrc. Mine sorts messages and adds them to suitable
MH folders, for example.

When mail is sent it goes:

	Sender MUA -> local MTA -> remote MTA -> remote MDA -> receiver MUA

So procmail generally only gets applied to incoming email.

Tet

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