使用linux自带的邮件功能测试邮件发送功能如下：
$ mail -s test xxx@163.com
sldkfjlskdjf[CTRL+D]
cc:
有时会出再提示:
You have a new mail in /var/spool/mail/root
并且在邮箱中看不到邮件；
解决办法:
1.查看出错的日志
$ tail -n 50 /var/spool/mail/root
From MAILER-DAEMON@ltv_73 Thu Dec 12 11:35:28 2013
Return-Path: <MAILER-DAEMON@ltv_73>
Received: from localhost (localhost)
by ltv_73 (8.13.8/8.13.8) id rBC3ZSPe006446;
Thu, 12 Dec 2013 11:35:28 +0800
Date: Thu, 12 Dec 2013 11:35:28 +0800
From: Mail Delivery Subsystem <MAILER-DAEMON@ltv_73>
Message-Id: <201312120335.rBC3ZSPe006446@ltv_73>
To: <root@ltv_73>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary="rBC3ZSPe006446.1386819328/ltv_73"
Subject: Returned mail: see transcript for details
Auto-Submitted: auto-generated (failure)
This is a MIME-encapsulated message
--rBC3ZSPe006446.1386819328/ltv_73
The original message was received at Thu, 12 Dec 2013 11:35:18 +0800
from 41_154 [127.0.0.1]
----- The following addresses had permanent fatal errors -----
(reason: 530 5.7.1 Client was not authenticated)
----- Transcript of session follows -----
... while talking to mail.163.com.:
>>> MAIL From:<root@ltv_73> SIZE=519
<<< 530 5.7.1 Client was not authenticated
554 5.0.0 Service unavailable
--rBC3ZSPe006446.1386819328/ltv_73
Content-Type: message/delivery-status
Reporting-MTA: dns; ltv_73
Received-From-MTA: DNS; sohu_41_154
Arrival-Date: Thu, 12 Dec 2013 11:35:18 +0800
Final-Recipient: RFC822; xxx@163.com
Action: failed
Status: 5.7.1
Diagnostic-Code: SMTP; 530 5.7.1 Client was not authenticated
Last-Attempt-Date: Thu, 12 Dec 2013 11:35:28 +0800
也可以用“-v" 参数来查看返回信息：
$ mail -v -s "test" xxx@163.com
返回中如果有”WARNING: local host name (ltv_13) is not qualified; see cf/README: WHO AM I?”，
是警告，可以不用管；
2.修改DNS
$ vim /etc/resolv.conf
修改成可用的DNS，这个地方的修改保存后即生效;
3.修改主机名【也可不做这一步】
$ sysctl kernel.hostname=newhostname
4.重启邮件服务
$ service sendmail restart
Linux sendmail发送邮件失败诊断案例：http://www.linuxdiyf.com/linux/13511.html
4个开源的命令行邮件客户端：http://www.linuxdiyf.com/linux/13910.html
Linux安全狗提示email not work不能发邮件解决方法：http://www.linuxdiyf.com/linux/12763.html
在Linux中加密邮件：http://www.linuxdiyf.com/linux/10373.html
4个可以发送完整电子邮件的命令行工具：http://www.linuxdiyf.com/linux/12327.html