diff -Naur cyrus-imapd-2.4.20.orig/imap/annotate.c cyrus-imapd-2.4.20/imap/annotate.c
--- cyrus-imapd-2.4.20.orig/imap/annotate.c	2017-08-18 02:29:14.000000000 +0200
+++ cyrus-imapd-2.4.20/imap/annotate.c	2017-08-21 17:12:57.000000000 +0200
@@ -1834,6 +1834,9 @@
     { "/vendor/cmu/cyrus-imapd/duplicatedeliver", ATTRIB_TYPE_BOOLEAN, BACKEND_ONLY,
       ATTRIB_VALUE_SHARED | ATTRIB_CONTENTTYPE_SHARED,
       ACL_ADMIN, annotation_set_mailboxopt, NULL },
+    { "/vendor/qmul/cyrus-imapd/lmtptarget", ATTRIB_TYPE_BOOLEAN, BACKEND_ONLY,
+      ATTRIB_VALUE_SHARED | ATTRIB_CONTENTTYPE_SHARED,
+      ACL_ADMIN, annotation_set_todb, NULL },
     { NULL, 0, ANNOTATION_PROXY_T_INVALID, 0, 0, NULL, NULL }
 };
 
diff -Naur cyrus-imapd-2.4.20.orig/imap/mboxlist.c cyrus-imapd-2.4.20/imap/mboxlist.c
--- cyrus-imapd-2.4.20.orig/imap/mboxlist.c	2017-08-18 02:29:14.000000000 +0200
+++ cyrus-imapd-2.4.20/imap/mboxlist.c	2017-08-21 17:14:22.000000000 +0200
@@ -884,6 +884,7 @@
     int isremote = 0;
     const char *p;
     mupdate_handle *mupdate_h = NULL;
+    struct annotation_data attrib;
 
     if (!isadmin && force) return IMAP_PERMISSION_DENIED;
 
@@ -903,6 +904,14 @@
 	if (!isadmin) { r = IMAP_PERMISSION_DENIED; goto done; }
     }
 
+    /* Does mailbox have the lmtptarget annotation set? */
+    if (annotatemore_lookup(name, "/vendor/qmul/cyrus-imapd/lmtptarget", "", &attrib) == 0 &&
+	attrib.value && !strcasecmp(attrib.value, "true")) {
+	/* Even admins can't delete a mailbox with the lmtptarget annotation set. */
+	r = IMAP_MAILBOX_NOTSUPPORTED;
+	goto done;
+    }
+
     r = mboxlist_mylookup(name, &mbentry, NULL, 1);
     if (r) goto done;
 
@@ -1003,6 +1012,7 @@
     char *newpartition = NULL;
     char *mboxent = NULL;
     mupdate_handle *mupdate_h = NULL;
+    struct annotation_data attrib;
 
     /* 1. open mailbox */
     r = mailbox_open_iwl(oldname, &oldmailbox);
@@ -1096,6 +1106,14 @@
 	}
     }
 
+    /* Does mailbox have the lmtptarget annotation set? */
+    if (annotatemore_lookup(oldname, "/vendor/qmul/cyrus-imapd/lmtptarget", "", &attrib) == 0 &&
+	attrib.value && !strcasecmp(attrib.value, "true")) {
+	/* Even admins can't rename a mailbox with the lmtptarget annotation set. */
+	r = IMAP_MAILBOX_NOTSUPPORTED;
+	goto done;
+    }
+
     r = mboxlist_mycreatemailboxcheck(newname, 0, partition, isadmin, 
 				      userid, auth_state, NULL, 
 				      &newpartition, 1, 0, forceuser, NULL);
diff -Naur cyrus-imapd-2.4.20.orig/perl/imap/IMAP/Admin.pm cyrus-imapd-2.4.20/perl/imap/IMAP/Admin.pm
--- cyrus-imapd-2.4.20.orig/perl/imap/IMAP/Admin.pm	2017-08-18 02:29:14.000000000 +0200
+++ cyrus-imapd-2.4.20/perl/imap/IMAP/Admin.pm	2017-08-21 17:12:57.000000000 +0200
@@ -788,6 +788,7 @@
 		 "expire" => "/vendor/cmu/cyrus-imapd/expire",
 		 "news2mail" => "/vendor/cmu/cyrus-imapd/news2mail",
 		 "sharedseen" => "/vendor/cmu/cyrus-imapd/sharedseen",
+		 "lmtptarget" => "/vendor/qmul/cyrus-imapd/lmtptarget",
 		 "sieve" => "/vendor/cmu/cyrus-imapd/sieve",
 		 "squat" => "/vendor/cmu/cyrus-imapd/squat" );