Mailstore

The basic function of the mailstore, sometimes incorrectly referred to as the mail server, is to store and send email to users via IMAP, POP, and web mail. The Sun ONE Messaging Server software is somewhat unique among the messaging systems on the market. Most messaging systems store email in a file system only or within a database only. The Messaging Server system offers a hybrid approach, storing messages in a file system, but also storing a copy of the header information (date, time, subject, sender, and so forth) in a database. This improves performance so that when users log in or sort email in their client, very little if any file system interaction is necessary. The information all comes from the database, which should be mostly in memory.

Mailstores can often be hundreds of gigabytes due to requirements for archiving and the volume and size of email messages these days, as outlined in the first chapter. It is not uncommon to find terabyte-sized mail stores, for example:

50,000 mailboxes * 20-megabyte quota = 1,000,000 megabytes = 1000 gigabytes = 1 terabyte