linux 中对外通信命令有:mail write wall talk mesg
 
1. mail --发送/接收邮件
a. 给系统或其他帐号发送邮件: mail 用户帐号
b. 收取邮件: mail
如: $ mail
Mail version 8.1 6/6/93.  Type ? for help.
"/var/spool/mail/magj": 3 messages 1 new 3 unread
 U  1 MAILER-DAEMON@erp202  Wed Aug 20 09:29 118/2820  "Returned mail: se"
 U  2 MAILER-DAEMON@erp202  Wed Aug 20 09:35  69/2521  "Returned mail: se"
>N  3 magj@erp202.  Mon Aug 25 13:43  16/662   "Meeting"
&
U 表示已读
N 表示未读
c. 邮件箱 $ mail  --读取用户系统邮箱
                 $ mail -f  --读取用户个人邮箱
d.  Mail   Commands
t <message list>                type messages
n                               goto and type next message
e <message list>                edit messages
f <message list>                give head lines of messages
d <message list>                delete messages
s <message list> file           append messages to file
u <message list>                undelete messages
R <message list>                reply to message senders
r <message list>                reply to message senders and all recipients
pre <message list>              make messages go back to /usr/spool/mail
m <user list>                   mail to specific users
q                               quit, saving unresolved messages in mbox
x                               quit, do not remove system mailbox
h                               print out active message headers
!                               shell escape
cd [directory]                  chdir to directory or home if none given
 
2. write  --给某个在线的用户发送即时消息, 接收消息的用户必须在线
 
3. wall  --向系统所有在线的用户发送广播消息
 
4.  talk   --向某个在线的用户发送聊天邀请, 退出邀请用Ctrl+C
 
5.  mesg --设置充许/禁止别的用户发送消息给你, 包括:wall, write, talk等.root 和 daemon发送的即时消息, 这个设置不起作用.
 
如:
$ mesg
is y