Introduced in release: 8.0.1
undeleteflag Message Store boolean option is set, it causes imapd to set an explicit
$undeleted message flag when the
\Deleted flag is removed. This feature allows clients to detect when a previously deleted message is no longer deleted, which can be helpful when providing a gateway to a protocol that has to treat this scenario as if a new message arrived. The
$undeleted message flag has no additional special semantics and may be set or cleared by clients if the IMAP ACL on the mailbox permits flag changes.
The default value is: 0