Understanding the Spool Directory MailSite uses a folder called 'Spool' by default as a staging post for messages in transmit through the system. This document briefly explains how the spool folder operates. For MailSite 9.2 and later, see KB 10379
Mail Spool Directory

You can use the Console to specify the Mail Spool Directory. The spool directory contains a number of subdirectories that are used as staging posts for messages. This folder needs permissions for which ever account the MailSite services are logged on under, default this will be SYSTEM. The MailSite installer will set the permissions for you.

The directory structure under the Mail Spool Directory is as follows.

Incoming

This directory holds messages received by the SMTPRA (Receiver Agent)service. For each message that is received by the server, the SMTPRA service will create a .msg file and a .rcp file and place it within the Incoming folder. The .msg file contains the message data, the .rcp file will contain the routing information. Both files will have the same name eg B000010020.msg & B000010020.rcp. The SMTPDA (Delivery Agent) also places messages here, for example, non-delivery reports and messages which are sent to mail lists.

Holding

The SMTP Delivery Agent moves messages from the incoming directory into this directory.

Domains

When a message is moved into the holding directory, the SMTP Delivery Agent creates a subdirectory within the domains directory for each separate domain to which the message is addressed. If the message is addressed to a local user, it creates a subdirectory called $local$. In each subdirectory it stores routing information and information about the message recipients in that domain. (The message itself stays in the holding directory.)

Dead

This directory collects messages which are both undeliverable and un-returnable.

lists

This directory contains subdirectories corresponding to mail lists. For every mail list, two directories are created: one corresponding to the list itself, and one corresponding to the -request address for the list. Messages are moved into these directories temporarily while they are being delivered to list members.