godaddy shared hosting.
wordpress multisite enabled.
plugins: Akismet(deactivated), Configure SMTP(deactivated), Hello Dolly(activated),Multisite User Management(activated), WP Mail SMTP(activated).
(I) Send all WordPress emails via SMTP
I have tried several mail service like gmail.com, qq.com, 163.com, most of the time I test sending mail it reported either connection refused, or timed out or things similar. Only two times it did pass the test and I registered successfully, but I didn't know why because next time it failed again.
(II)Use the PHP mail() function to send emails
The tests are perfect. When I registered new user, it worked occassionally, as above, and failed most of time.
I am totally lost. It seems to me more like an artwork than a technical issue. I am contacting godaddy support to see if they give me some clues.