I.e., I might do this, to make sure I don't have to worry about whether I use =
or .=
...
$headers = implode("\r\n", [
"MIME-Version: 1.0",
"Content-type:text/html;charset=UTF-8",
"From: user@example.com"
]);
...with the added benefit of making it easy to add, remove, or edit headers as/when needed.