H1: Response Code
H2: ESMTP
	450 Busy
450 means: mail box is temporally available
H2: POP3
	-ERR
	-ERR Busy
memo: there are no authorized resonse message for "busy".

H2: IMAP4
	BYE
	BYE [ALERT] Busy

H2: status
Listen
Established
Closed
Finwait2
Time_wait

look also: /sys/src/9/ip/tcp.c
char *tcpstates[] =
{
	"Closed", 	"Listen", 	"Syn_sent", "Syn_received",
	"Established", 	"Finwait1",	"Finwait2", "Close_wait",
	"Closing", 	"Last_ack", 	"Time_wait"
};