email server concept: what's mail delivery agent

[Patrick Welche]

This is the way I understand - this might be wrong too!

On Wed, Jun 02, 2004 at 07:49:53PM +0800, Zhang Weiwu wrote:
> 1. Moden mail servers don't often do mail forwarding. So upon receiving 
> an email, it will always be 'local delievery'.;

I understand local delivery to mean "write this message to a file".
This is different to "pass this message on to cyrus".

> 2. Documents often mention 'delivery agent' and 'maildir', it seems 
> 'delivery agent' is not a standalone package, there is a delievery agent 
> in postfix package, and there is also one in cyrus package, I can choose 
> to use the delivery agent (postfix's or cyrus')

I think postfix can deliver directly to cyrus, i.e., not need to pipe
the message to cyrus' deliver (don't know for sure, I use exim).

> 3. maildir is a way to store email, it is where postfix save incoming 
> mail, and it is the place cyrus-imapd get emails so that to put to 
> user's INBOX. But an email server can have no maildir completely, and 
> let cyrus's delivery agent by pass maildir and put mail directly to 
> user's INBOX.

Yes, maildir is a filesystem storage format. If postfix is going to
deliver all local mail to cyrus, then cyrus will be using its filesystem
format, which I think is similar to maildir: one directory per folder,
messages as numbered files.

> 4. putting the incoming emails in to each coorisponding domain's email 
> storage place is the job of delivery agent.

It is up to postfix to sort out where each message should be delivered to
according to domain. cyrus can be set up to appear as several domains (just
to confuse ;) )

Cheers,

Patrick
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