zmprov modifyServer {{ you domain }} zimbraMtaTlsAuthOnly FALSE
zmcontrol restart

查看对应配置

zmprov getServer {{ you domain }} | grep Auth

查看SMTP是否开启成功

[zimbra@xxxxx log]$ telnet localhost 25
Trying 127.0.0.1…
Connected to localhost.
Escape character is '^]'.
220 xxxx ESMTP Postfix
ehlo xxxx
250-xxxxx
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH LOGIN PLAIN #SMTP认证相关参数
250-AUTH=LOGIN PLAIN #SMTP认证相关参数
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN