The Internet RFC 2086, IMAP4 ACL Extension,
is the standard that defines the access control lists (ACLs) used in the IMAP4 protocol. The Message Server has supported RFC2086 since version 5.0.
RFC2086 describes the ACL as a set of identifier and rights pairs. For our purposes, the user ID for the IMAP user is the identifier.
The standard rights defined are:
l - lookup (mailbox is visible to LIST and LSUB commands)
r - read (SELECT the mailbox, perform CHECK, FETCH, PARTIAL, SEARCH, COPY from mailbox)
s - keep seen/unseen information across sessions (STORE SEEN flag)
w - write (STORE flags other than SEEN and DELETED)
i - insert (perform DELETED, COPY into mailbox)
p - post ...