/root @ rhel7 ~ # systemctl start postfix
Job for postfix. The service failed because the control process exited with the error code. See "systemctl status postfix. Service" and "journalctl - xe" for details.
/root @ rhel7 ~ # systemctl status postfix
Postfix. Service - postfix Mail Transport Agent
The Loaded: the Loaded (/usr/lib/systemd/system/postfix. Service; Enabled. Vendor preset: disabled)
Active: failed (Result: exit - code) since Sun 18:45:54 2020-02-23 CST; Line 7 s
Process: 36203 ExecStart=/usr/sbin/postfix start (code=exited, status=1/FAILURE)
Process: 36201 ExecStartPre=/usr/libexec/postfix/chroot - update (code=exited, status=0/SUCCESS)
Process: 36199 ExecStartPre=/usr/libexec/postfix aliasesdb (code=exited, status=0/SUCCESS)

Feb 23 18:45:53 rhel7.6 systemd [1] : Starting Postfix Mail Transport Agent...
Feb 23 18:45:53 rhel7.6 postfix [36203] : warning: valid_hostname: numeric hostname: 6
Feb 23 18:45:53 rhel7.6 postfix [36203] : fatal: the file/etc/postfix/main cf: parameter mydomai... 6:
Feb 23 18:45:54 rhel7.6 systemd [1] : postfix. Service: control the process exited, code=exited the status=1
Feb 23 18:45:54 rhel7.6 systemd [1] : Failed to start Postfix Mail Transport Agent.
Feb 23 18:45:54 rhel7.6 systemd [1] : Unit postfix. Service rose failed state.
Feb 23 18:45:54 rhel7.6 systemd [1] : postfix. The service failed.
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