Let's walk through why your contact form is showing a blank page when submitted, and fix it up properly:

1. Critical Mismatch in Form Field Name #

Your HTML uses name="mail" for the email input, but your PHP code checks for isset($_POST['email']) — this condition will never be true, so all the email-sending logic gets skipped entirely, leaving you with a blank page.

Fix: #

Update the PHP condition to check for the correct field name:

if(isset($_POST['mail']) && !empty($_POST['mail'])){

2. Invalid Email Header Format #

Your email headers use plain line breaks instead of the required \r\n (RFC-compliant line endings for email headers). Also, there's a typo: X=Mailer should be X-Mailer.

Fix: #

Rewrite the header line with proper formatting:

$header = "From:info@diegodiasp.com\r\n"
         ."Reply-To:".$email."\r\n"
         ."X-Mailer:PHP/".phpversion();

3. Enable Error Reporting for Debugging (Critical for Live Sites) #

Live servers often disable error display by default, which hides issues that cause blank pages. Add these lines at the top of your contactform.php to see what's going wrong:

error_reporting(E_ALL);
ini_set('display_errors', 1);

Once you've fixed the issues, you can remove these lines (or set display_errors to 0 for production).

4. Improved Security & Readability #

• Replace addslashes() with htmlspecialchars() to prevent XSS risks when handling user input:

  $name = htmlspecialchars($_POST['name']);
  $email = htmlspecialchars($_POST['mail']);
  $message = htmlspecialchars($_POST['message']);
  

• Use PHP_EOL for line breaks in the email body (cross-platform compatible):

  $body = "Name: ".$name.PHP_EOL
         ."Email: ".$email.PHP_EOL
         ."Message: ".$message;
  

Full Corrected PHP Code #

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

if(isset($_POST['mail']) && !empty($_POST['mail'])){
    $name = htmlspecialchars($_POST['name']);
    $email = htmlspecialchars($_POST['mail']);
    $message = htmlspecialchars($_POST['message']);

    $to = "info@diegodiasp.com";
    $subject = "Contact - Diego Dias Front End";
    $body = "Name: ".$name.PHP_EOL
           ."Email: ".$email.PHP_EOL
           ."Message: ".$message;
    $header = "From:info@diegodiasp.com\r\n"
             ."Reply-To:".$email."\r\n"
             ."X-Mailer:PHP/".phpversion();

    if(mail($to,$subject,$body,$header)){
        echo("Email successfully sent!");
    }else{
        echo("Email not sent!");
    }
}
?>

Additional Notes #

• If the mail still fails to send, check your hosting provider's mail configuration — some shared hosts require you to use a verified sender email that matches your domain.
• Consider adding form validation on the frontend (e.g., required attributes, email format checks) to catch issues before submission:

  <input class="form-control" name="name" placeholder="Your Name" required>
  <input class="form-control" name="mail" placeholder="Your Email" type="email" required>
  

内容的提问来源于stack exchange，提问作者Diego Dias