Resolve VESTACP The "error:xxx is not valid" problem when adding users

The error:xxx is not valid mailbox was not recognized when the user was added. It suddenly occurred to me that it was not a DNS problem.
Use the View Cat command directly to view

Cat/etc/resolv.conf
dns-127.0.0.1

The DNS server is found to be a local address. So direct use of the command to replace the DNS server with Google DNS. You can also modify the resolv.conf file yourself.

echo "NameServer 8.8.8.8" >/etc/resolv.conf

Modify the Restart DNS server

Service named restart

Then add the user again