为什么PHP无法从test@test.com发送邮件？

This doesn't work:

$to = 'myemail@gmail.com';
$from = 'test@test.com';
$subj = 'test';
$message = 'hello';

$headers =  "From: {$from}
" .
            "Reply-To: {$from}
";
            "X-Mailer: PHP/" . phpversion();

$response['success'] = mail($to, $subj, $message, $headers);

This does:

$to = 'myemail@gmail.com';
$from = 'bill@gates.com';
$subj = 'test';
$message = 'hello';

$headers =  "From: {$from}
" .
            "Reply-To: {$from}
";
            "X-Mailer: PHP/" . phpversion();

$response['success'] = mail($to, $subj, $message, $headers);

The mail function doesn't seem to work with test@test.com, is there a reason for this ?

Thank you

Probably because test.com has an SPF record which indicates that it doesn't send email:

test.com.       7200    IN  TXT "v=spf1 ~all"

This would likely lead GMail to reject (or flag as spam) any mail claiming to be from test.com.

Alternatively, GMail may have an explicit block on test@test.com. :)

test2.com is not a valid domain name.MTA probably refuse to relay your message because of that.

If you turn on error_reporting, are you receive any warning?