Sealed System Design

Cyrus IMAP is designed to run on sealed system, meaning that no user-related information needs to be available to the POSIX system, aside from the user and group Cyrus IMAP itself runs under.

This eliminates the requirement for any of the service’s users to hold POSIX account information attributes, and eliminates the need for Cyrus IMAP to maintain a super-privileged process allowed to substitute user.

The message spool directory or directories are held privately by the Cyrus IMAP software, and can be accessed by user through IMAP, POP, NNTP or KPOP protocols.

This design concept vastly increases the efficiency, scalability and security of Cyrus IMAP, and makes it easier to configure, maintain, troubleshoot and administer a Cyrus IMAP environment.


Since all files and directories are held by the user and group that Cyrus IMAP runs under, any filesystem quota being used does not apply to anyone other than this user and group, voiding the ability to count disk usage towards a billing account’s quota.

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