我用post和action方法來發(fā)送郵件。我嘗試通過運行測試 PHP 從托管服務(wù)器發(fā)送短郵件。它正在工作。將其與 HTML 表單合并后不起作用，并且還給出錯誤未定義的索引。這是代碼的摘要。HTML 文件：     <form id="msform" action="./php/mailer.php" name="step1"  method="POST">          <fieldset>        <h2 class="fs-title">Fillup basic Information</h2>        <h3 class="fs=subtitle">This is step 1</h3><br>        <input type="text" name="fname" placeholder="First Name" required/>        <input type="text" name="lname" placeholder="Last Name" required/> <input type="button" name="next" class="next action-button"  value="Next" onclick="return validateStep1()"/>     </fieldset>    </from>PHP 文件：<?phpif(isset($_POST['next'])){$fname = $_POST['fname'];$lname = $_POST['lname'];  $msg="Hello My Name is $fname $lname . My Company is $company which is located in $address1 . The Second address is $address2. I live in $city city, $state state, $zip zip, $country.  My Phone number is $tel. My Fax number is $fax. My email is $email. I want to donate $other. My Custom Donate is $otherDonation. I want to donate regular=$regulardonate for $dollar dollar  per $months";  mail("x@gmail.com","Donation",$msg);}?>JS文件：function validateStep1(){  var fname =document.forms["step1"]["fname"];  var lname =document.forms["step1"]["lname"];if (fname.value == "")                                    {       window.alert("Please enter your first name.");       fname.focus();      return false;   }   if (lname.value == "")                                    {       window.alert("Please enter your Last name.");       lname.focus();       return false;   }     window.open('./second.html', '_self');  return true;   }我在 GitHub 上的 Live 表單，您可以查看 - https://tamzid958.github.io/multipage_form/