'Order-mail format: HTML mail' is not working

[crystal_moon]

VM: 3.0.12
Joomla 3.4.8
PHP: 5.4 Native

When I tested the shop or changed order status, e-mail of the order don't come to administrator and customer.
It works fine if 'Order-mail format: Text mail'.

Please tell me what I should do

[jenkinhill]

Are you using overrides?

[crystal_moon]

No. I did not edit anything in the core