@takayukister Why do you keep refer to the “Failed to send your message” FAQ page? Which doesn’t help at all.
The error message is “There was an error trying to send your message. Please try again later”
The FAQ page you referred to doesn’t help with this problem
I got the same problem.
Strangely, it all works on my local developing system within the office local domain: wordpress-dev/wordpress
However, after I pushed it to the live site http://www.outwebsite.com it gave me the aforementioned error message.