PHP Manual: Sets the ACL for a given mailbox

bool imap_setacl(
    IMAP\Connection $imap,
    string $mailbox,
    string $user_id,
    string $rights
)

Sets the ACL for a giving mailbox.

imap: An IMAP\Connection instance.
mailbox: The mailbox name, see imap_open for more information

Warning
Passing untrusted data to this parameter is insecure, unless imap.enable_insecure_rsh is disabled.
user_id: The user to give the rights to.
rights: The rights to give to the user. Passing an empty string will delete acl.

Returns true on success or false on failure.

Version	Description
8.1.0	The `imap` parameter expects an IMAP\Connection instance now; previously, a valid `imap` resource was expected.

This function is currently only available to users of the c-client2000 or greater library.

imap_setacl