On a share folder, when you configure the access right for someone, they are a difference between select every check-box and select the square button on the top.
When select every check-box you got

lrswipktcda

access right for the folder. When selecting the square button on the top you got

lrswipkxtecda

access right. So they are missing the «x» and the «e» who stand for

x : Use the x right to indicate the ACI subject has the right to DELETE the folder on which the ACL is set, as opposed to the now obsolete c right or d right.

and

e:Stands for expunge.

The ACI subject is allowed to expunge messages in this folder, meaning the ACI subject has the right to remove all messages that have been flagged as \Deleted from all visibility.

In IMAP, expunging messages only applies to messages flagged as \Deleted. For the ACI subject to be able to flag messages as \Deleted however, the t right is required.

We say “remove from all visibility”, because the implementation of expunging messages in Cyrus IMAP is subject to the expunge_mode setting in imapd.conf(5), which when set to delayed only causes the reference to the expunged messages to be deleted from the folder index database – effectively removing the expunged message(s) from all visibility, while the individual message files remain in place on the Cyrus IMAP server filesystem.