Outbound mail (SMTP port 25) seems to be blocked by your network. You will not be able to send any mail. Many residential networks block port 25 to prevent hijacked machines from being able to send spam. A quick connection test to Google’s mail server on port 25 failed.
Ping gmail in China sometimes, sometimes not!
Can I customize the test port 25 port URL?
To what end??? You need port 25 to be able to communicate with other mail servers. If your provider has blocked it, see what the procedure is to get that port unblocked. If your provider will not unblock it, move on to a different provider.
MIAB send and receive mail normally
The server has been in China!
Google is restricted, ping gmail in China sometimes can sometimes not!
If you change to a test in China, such as mail.aliyun.com, it is normal
Network // sometimes
✓ Firewall is active.
✓ Outbound mail (SMTP port 25) is not blocked.
✓ IP address is not blacklisted by zen.spamhaus.org.
Continue testing
Network // MIAB mail sending and receiving everything is normal
✓ Firewall is active.
Outbound mail (SMTP port 25) seems to be blocked by your network. You will not be able to send any mail. Many residential networks block port 25 to prevent hijacked machines from being able to send spam. A quick connection test to Google’s mail server on port 25 failed.
✓ IP address is not blacklisted by zen.spamhaus.org.