A remote user is capable of crashing Alt-N MDaemon 220.127.116.11 by executing the pass command, then the UIDL command and quitting the mail server before the UIDL has returned a response. This must be done before the user is presented with the POP3 login banner. Restarting the application is required in order to regain normal functionality.
Perform the following very quickly:
+OK <target> POP service ready using MDaemon
+OK <username>... Recipient ok
-ERR that command is valid only in the AUTHORIZATION state!
-ERR unknown POP command!
+OK <username> <target> POP Server signing off (mailbox empty)