I solved the QMail problems encountered by mail.ahhf-l-tax.gov.cn.

1, "deferral: Uh-oh:_home_directory_is_writable._(#4.7.0)"
Answer: 
cd /home/vpopmail/domains
chmod 700 ahhf-l-tax.gov.cn
cd ahhf-l-tax.gov.cn
chmod -R 777 *
chmod 600 .qmail-default

then you can test by:
echo to: tw | /qmail/bin/qmail-inject
tail /var/log/maillog
You can see the status from the log.

2, another problem: "deferral: CNAME_lookup_failed_temporarily._(#4.4.3)"
Phenemon: can send and receive among the local domain, can receive from external, but cannot send to external.
Answer:
In the /etc/resolv.conf,  add
nameserver the ip of the DNS server