diff --git a/server/mailserver/mail/mailmgr.go b/server/mailserver/mail/mailmgr.go
index 282c8f1e..68c52cb5 100644
--- a/server/mailserver/mail/mailmgr.go
+++ b/server/mailserver/mail/mailmgr.go
@@ -16,11 +16,11 @@ type userGroup struct {
 }
 
 type mailMgr struct {
-	idHash sync.Map
-	wholeMails sync.Map
-	groupMails sync.Map
-	personalMails sync.Map
-	groupHash sync.Map
+	idHash sync.Map //int64 => *mail
+	wholeMails sync.Map //int64 => *mail
+	groupMails sync.Map //int64 => *mail
+	personalMails sync.Map //string => sync.Map<int64, *mail>
+	groupHash sync.Map //int64 => *userGroup
 }
 
 func (this *mailMgr) Init() {