HTML mail Template's test mail is not working.

Hello.

I hope you having good day.
I am experiencing a problem now.
I tried use HTML Email Template for my customer.
The test mail can be sent, but the mail result is strange.
It might be not working?
The mail's content was.......

This is a test message I want to try out to see if it works
Is it working well?

I grant an access.
King Regards
KAZUKI