Allow all numeric mailbox names

[ram]

How do I allow all numeric mailbox names in cyrus 

On my old cyrus imapd server( 2.2.38)  when I create a numeric mailbox
and try logging in on pop I get an error immediately after giving
username 


[root at netserv root]# telnet localhost 110
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
+OK POP3 server ready
user 821012
-ERR [AUTH] Invalid user