[root@server ]# Could not resolve host: smtp.qq.com "/root/dead.letter" 11/296 . . . mes

報錯：

[root@server ]# Could not resolve host: smtp.qq.com
"/root/dead.letter" 11/296
. . . message not sent.

原因與解決：

1.DNS解析出現錯誤

[root@server ~]# cat /etc/resolv.conf 
# Generated by NetworkManager
nameserver 8.8.8.8
[root@server ~]# ping www.baidu.com
PING www.a.shifen.com (36.152.44.96) 56(84) bytes of data.
64 bytes from 36.152.44.96 (36.152.44.96): icmp_seq=1 ttl=128 time=9.02 ms
64 bytes from 36.152.44.96 (36.152.44.96): icmp_seq=2 ttl=128 time=21.2 ms
^C
--- www.a.shifen.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 9.021/15.136/21.252/6.116 ms
[root@server ~]# 

2.25端口沒開

[root@server ~]# netstat -natp | grep 25
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1154/master         
tcp6       0      0 ::1:25                  :::*                    LISTEN      1154/master         
[root@server ~]# 

3.關閉防火牆和SElinux
 

systemctl stop firewalld
setenforce 0