Step 1 : first please create your client ID and client secrete key using below given url.
Step 2 : https://developers.google.com/gmail/
Step 3 : you will get client id and secrete key from there and call back url.
Step 4 : After all this Please copy this code and paste your file and put client id, secrete key and call back url.

Gmail Credential Page :

<?php
$client_id = Put your client Id; // '**************0gd4lvravm92ui60d6pl.apps.googleusercontent.com';
$client_secret = Put your gmail secret; '654646464646QgcsMiv_I'; 
$redirect_uri = Put your callback URL;
$max_results = 500; //set the Maximum result you want to fetch
 
$auth_code='';
if(isset($_GET["code"])) 
{
 $auth_code = $_GET["code"];
 function getContent($url)
 {
 $curl = curl_init();
 //The URL to fetch.
 curl_setopt($curl,CURLOPT_URL,$url); 
 //TRUE to return the transfer as a string of the return value of curl_exec() instead of outputting it out directly.
 curl_setopt($curl,CURLOPT_RETURNTRANSFER,TRUE); 
 //The number of seconds to wait while trying to connect.You can use 0 to wait indefinitely.
 curl_setopt($curl,CURLOPT_CONNECTTIMEOUT,5); 
 //Set the contents of "User-Agent: " which will used in a HTTP request.
 $userAgent = $_SERVER["HTTP_USER_AGENT"];
 curl_setopt($curl, CURLOPT_USERAGENT, $userAgent); 
 //Set this TRUE To follow any "Location: " header that the server sends as part of the HTTP header.
 curl_setopt($curl, CURLOPT_FOLLOWLOCATION, TRUE); 
 //To automatically set the Referer: field in requests where it follows a Location: redirect.
 curl_setopt($curl, CURLOPT_AUTOREFERER, TRUE); 
 //The maximum number of seconds to allow cURL functions to execute.
 curl_setopt($curl, CURLOPT_TIMEOUT, 10); 
 //Set this false to stop cURL from verifying the peer's certificate.
 curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
 $contents = curl_exec($curl);
 curl_close($curl);
 return $contents;
 }
 
 $fields=array(
 'code'=> urlencode($auth_code),
 'client_id'=> urlencode($client_id),
 'client_secret'=> urlencode($client_secret),
 'redirect_uri'=> urlencode($redirect_uri),
 'grant_type'=> urlencode('authorization_code')
 );
 $post = '';
 foreach($fields as $key=>$value) { $post .= $key.'='.$value.'&'; }
 $post = rtrim($post,'&');
 $curl = curl_init();
 curl_setopt($curl,CURLOPT_URL,'https://accounts.google.com/o/oauth2/token');
 curl_setopt($curl,CURLOPT_POST,5);
 curl_setopt($curl,CURLOPT_POSTFIELDS,$post);
 curl_setopt($curl, CURLOPT_RETURNTRANSFER,TRUE);
 curl_setopt($curl, CURLOPT_SSL_VERIFYPEER,0);
 curl_setopt($curl, CURLOPT_SSL_VERIFYHOST,0);
 $result = curl_exec($curl);
 curl_close($curl);
 
 $response = json_decode($result);
 $accesstoken = $response->access_token;
 
$url = 'https://www.google.com/m8/feeds/contacts/default/full?&alt=json&max-results='.$max_results.'&oauth_token='.$accesstoken;
$xmlresponse = getContent($url);
 
 if((strlen(stristr($xmlresponse,'Authorization required'))>0) && (strlen(stristr($xmlresponse,'Error '))>0))
 {
 echo "There is some error.Try reloading the page.";
 exit();
 }
 
 /*Custom Coding*/
 if(count($xmlresponse)>0)
 {
 $decoded_data=json_decode($xmlresponse);
 echo '<table cellpadding="0" cellspacing="0">'; 
 echo '<tr>
 <th style="padding: 3px;border-top: 1px solid #000;border-left: 1px solid #000;border-bottom: 1px solid #000;font-family: arial;font-size: 13px;">Email Address</th>
 
 </tr>';
 foreach($decoded_data->feed->entry as $k=>$v)
 {
 $email_address=isset($v->{'gd$email'}[0]->address)?$v->{'gd$email'}[0]->address:'';
 $UserName=isset($v->title->{'$t'})?ucwords(strtolower($v->title->{'$t'})):'';
 $ContactNo=isset($v->{'gd$phoneNumber'}[0]->{'$t'})?$v->{'gd$phoneNumber'}[0]->{'$t'}:'';
 echo '<tr>
 
 <td style="padding: 3px;border-left: 1px solid #000;border-bottom: 1px solid #000;font-family: arial;font-size: 13px;">'.$email_address.'</td>
 
 </tr>'; 
 }
 echo '</table>';
 }
 
} else {
?>
<a href="https://accounts.google.com/o/oauth2/auth?client_id=<?php echo $client_id;?>&redirect_uri=<?php echo $redirect_uri;?>&scope=https://www.google.com/m8/feeds/&response_type=code">Import Gmail Contact</a>
<?php
}
?>

OUTPUT : You Will get all mail like this.