仅在按下“提交”按钮且表单有效后，才尝试使用PHP发送电子邮件

请试试：

<?php
  //Set main variables for the data.
  $fname = $lname = $email = $subject = $website = $likedsite = $findoption = $comments = "";

  //Set the empty error variables.
  $fnameErr = $lnameErr = $emailErr = $subjectErr = $commentsErr = $websiteErr = $findoptionErr = "";

  //Initialize variable used to identify form is valid OR not. 
  $formValid = true;

  //Check to see if the form was submitted.
  if ($_SERVER["REQUEST_METHOD"] == "POST")
  {
    //Check the 'First Name' field.
    if (empty($_POST["fname"]))
    {
      $formValid = false;//Form not validate
      $fnameErr = "First Name is Required.";
    } 
    else
    {
      $fname = validate_info($_POST["fname"]);
    }

    //Check the 'Last Name' field.
    if (empty($_POST["lname"]))
    {
      $formValid = false;//Form not validate
      $lnameErr = "Last Name is Required.";
    } 
    else
    {
      $lname = validate_info($_POST["lname"]);
    }

    //Check the 'E-Mail' field.
    if (empty($_POST["email"]))
    {
      $formValid = false;//Form not validate
      $emailErr = "E-Mail is Required.";
    } 
    else
    {
      $email = validate_info($_POST["email"]);
      //Check if valid email.
      if (!filter_var($email, FILTER_VALIDATE_EMAIL))
      {
        $formValid = false;//Form not validate
        $emailErr = "Invalid E-Mail Format.";
      }
    }

    //Check the 'Subject' field.
    if (empty($_POST["subject"]))
    {
      $formValid = false;//Form not validate
      $subjectErr = "Subject is Required.";
    } 
    else
    {
      $subject = validate_info($_POST["subject"]);
    }

    //Check the 'Website' field.
    if (empty($_POST["siteurl"]))
    {
      $website = "";
    } 
    else
    {
      $website = validate_info($_POST["siteurl"]);
      //Check if valid URL.
      if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website))
      {
        $formValid = false;//Form not validate
        $websiteErr = "Invalid URL.";
      }
    }

    //Check the 'How Did You Find Us' options.
    if (empty($_POST["howfind"]))
    {
      $formValid = false;//Form not validate
      $findoptionErr = "Please Pick One.";
    } 
    else
    {
      $findoption = validate_info($_POST["howfind"]);
    }

    //Check the comment box.
    if (empty($_POST["questioncomments"]))
    {
      $formValid = false;//Form not validate
      $commentsErr = "Questions/Comments are Required.";
    } 
    else
    {
      $comments = validate_info($_POST["questioncomments"]);
    }

    //Pass any un-required data.
    $likedsite = validate_info($_POST["likedsite"]);
  }


  //If every variable value set, send mail OR display error...
  if (!$formValid){
     echo"Form not validate...";

  } 
  else {
      //Make the message.
      $message =
      "
      First Name: $fname.\n
      Last Name: $lname.\n
      Website: $website\n
      Did They Like the Site? $likedsite.\n
      How They Found Us. $findoption.\n
      Question/Comments:\n
      $comments.
      ";
      $message = wordwrap($message, 70);
      $headers = "From: $email";

      mail("[email protected]", $subject, $message, $headers);


      if($sendMail){
        echo "Mail Sent!!";
      }
      else {
        echo "Mail Not Sent!!";
      }
  }

  function validate_info($data) {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
  }
?>

我根据一些更改来编辑答案。现在，此代码仅在表单必填字段不为空且所有字段值均按照验证有效时才允许发送邮件。

让我知道是否有任何问题。