sendmail 在一段时间后停止发送电子邮件

Question

我全新安装了 CentOS 7（按照 howtoforge 上的指南操作https://www.howtoforge.com/perfect-server-centos-7-apache2-mysql-php-pureftpd-postfix-dovecot-and-ispconfig3) 并且它有 sendmail。问题是一段时间后 sendmail 停止发送电子邮件。我这样做之后，它就可以正常工作并发送队列中的所有邮件。但后来由于某种原因它再次停止发送电子邮件。

cd /etc/mail
make
make restart

这些是发送电子邮件失败时的内容

Mar 17 15:53:18 ******** postfix/smtpd[9868]: disconnect from localhost[127.0.0.1]
Mar 17 15:53:18 ******** sendmail[9948]: v2HCrIqC009948: from=********@gmail.com, size=245, class=0, nrcpts=1, msgid=<201703171253.v2HCrIqC009948@********.********>, relay=root@localhost
Mar 17 15:53:18 ******** postfix/smtpd[9868]: connect from localhost[127.0.0.1]
Mar 17 15:53:18 ******** sendmail[9948]: STARTTLS=client, relay=[127.0.0.1], version=TLSv1/SSLv3, verify=FAIL, cipher=****************-SHA384, bits=256/256
Mar 17 15:53:18 ******** postfix/smtpd[9868]: NOQUEUE: filter: RCPT from localhost[127.0.0.1]: <********@gmail.com>: Sender address triggers FILTER amavis:[127.0.0.1]:10026; from=<********@gmail.com> to=<********@gmail.com> proto=ESMTP helo=<********.********>
Mar 17 15:53:18 ******** postfix/smtpd[9868]: warning: hash:/etc/mailman/virtual-mailman is unavailable. open database /etc/mailman/virtual-mailman.db: No such file or directory
Mar 17 15:53:18 ******** postfix/smtpd[9868]: warning: hash:/etc/mailman/virtual-mailman lookup error for "********@gmail.com"
Mar 17 15:53:18 ******** postfix/smtpd[9868]: NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 451 4.3.0 <********@gmail.com>: Temporary lookup failure; from=<********@gmail.com> to=<********@gmail.com> proto=ESMTP helo=<********.********>
Mar 17 15:53:18 ******** sendmail[9948]: v2HCrIqC009948: to=********@gmail.com, ctladdr=********@gmail.com (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30245, relay=[127.0.0.1] [127.0.0.1], dsn=4.3.0, stat=Deferred: 451 4.3.0 <********@gmail.com>: Temporary lookup failure
Mar 17 15:53:18 ******** postfix/smtpd[9868]: disconnect from localhost[127.0.0.1]