sendmail: stat=Deferred: Connection refused by [127.0.0.1]

背景

为了防止服务器被脚本小子爆破决定使用fail2ban来加强服务器安全，fail2ban详细介绍可以参考https://github.com/fail2ban/fail2ban 。安装之前可以检查下sendmail是否安装，我个人习惯是sendmail和mailx都安装上：

[root@vps ~]# yum install sendmail mailx -y

安装完成后配置了sshd防爆破，IP封锁时间为1年（单位为妙）。过了几个小时，重新登录服务器，查看fail2ban的日志：

[root@vps ~]# tail -100 /var/log/fail2ban.log
Dec 11 21:30:36 iZ267p7uxilZ sendmail[3395]: u6T6Aiai006695: to=alert@domain.com, ctladdr=root (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30226, relay=[127.0.0.1] [127.0.0.1], dsn=4.0
.......................
Dec 11 21:45:01 iZ267p7uxilZ sendmail[3596]: u6T6Aiai006695: from=root, size=225, class="0", nrcpts=1, msgid=<201607290613.u6T6DmTF003596@git.xx.com>, relay=root@localhost
Dec 11 21:45:01 iZ267p7uxilZ sendmail[3596]: u6T6Aiai006695: to=alert@domain.com, ctladdr=root (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30225, relay=[127.0.0.1] [127.0.0.1], dsn=4.0
.......................
stat=Deferred: Connection refused by [127.0.0.1]

发现Linux用sendmail发信失败，提示Connection refused by [127.0.0.1]

解决方法

通过排查发现sendmail虽然安装了，但是服务没有启动，因为我有一个习惯那就是安装完软件后都会手动重启一下系统导致服务没有重启：

[root@vps ~]# systemctl status sendmail
● sendmail.service - Sendmail Mail Transport Agent
   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; disabled; vendor preset: disabled)
   Active: inactive (dead)
[root@vps ~]# systemctl start sendmail
[root@vps ~]# systemctl status sendmail
● sendmail.service - Sendmail Mail Transport Agent
   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; disabled; vendor preset: disabled)
   Active: active (running) since Sun 2023-12-11 19:39:44 CST; 3s ago
  Process: 154732 ExecStart=/usr/sbin/sendmail -bd $SENDMAIL_OPTS $SENDMAIL_OPTARG (code=exited, status=0/SUCCESS)
  Process: 154728 ExecStartPre=/etc/mail/make aliases (code=exited, status=0/SUCCESS)
  Process: 154726 ExecStartPre=/etc/mail/make (code=exited, status=0/SUCCESS)
 Main PID: 154757 (sendmail)
    Tasks: 1 (limit: 18770)
   Memory: 3.4M
   CGroup: /system.slice/sendmail.service
           └─154757 sendmail: accepting connections

添加开机启动：

[root@vps ~]# systemctl enable sendmail
[root@vps ~]# systemctl is-enabled sendmail.service
enabled