how to generate unsubscribe link for newsletter?

Generate a hash of the user id + some secret string, put the id and the hash to the link, and serve it using a script which would unsubscribe the user, after verifying the hash.

The hash doesn't have to be in a database, just compute it on the fly.

Script creating the unsubscribe link:

<?$link = "unsubscribe.php?id=$user['id']&validation_hash=".md5($user['id'].$SECRET_STRING)<a href="<?=$link?>">Unsubscribe</a>

Script processing the unsubscribe link:

function unsubscribe() {    $expected = md5( $user['id'] . $SECRET_STRING );    if( $_GET['validation_hash'] != $expected )        throw new Exception("Validation failed.");    sql("UPDATE users SET wants_newsletter = FALSE WHERE id = " . escape($_GET['id']);}

It's not the most secure thing ever, but good enough.

Yes it shoould be saved in a database. You should use something like wamp, lamp or xampp. These are local servers and gives you a mysql database (phpmyadmin) to work in.

to connect with the database, you can use this:

<?php    define("DB_HOST", "localhost");/*host*/    define("DB_USERNAME", "username");/*username*/    define("DB_PASSWORD", "pass123");/*password*/    define("DB_NAME", "mydatabase");/*database name*/    try    {        $db_conn = new PDO('pgsql:host='.DB_HOST.';dbname='.DB_NAME,DB_USERNAME,DB_PASSWORD);    }    catch(PDOException $e)    {        print "Error!:".$e->getMessage()."\n";        die();    }?>

then, you can try to create a new table in mysql like this:

CREATE TABLE subcribe(subscribeId     INT,emailadress     VARCHAR(60),....);

then, you can add a subscriber to your database like this:

if he logs in, you set a cookie for is emailadress:

setcookie('emailadress',$hisEmailadress,time()+3600);

then add subcriber:

  $emailadress=$_COOKIE['emailadress'];    $subscriberId = $db_conn->prepare('SELECT MAX(subscriberId) FROM subcribe');    $subscriberId ->execute();    $row = $subscriberId ->fetch(PDO::FETCH_BOTH);    $subscriberId = $row[0]+1;/*unique number because it's one higher then max*/        $subscriber = $db_conn->prepare("INSERT INTO subscribe(subscriberId, emailadress) VALUES('$subscriberId','$emailadress')");    $subscriber ->execute();

to unsubscribe, just do this:

$unsubscribe = $db_conn->prepare('DELETE FROM subscribe WHERE emailadress=:emailadress');$unsubscribe->bindParam(':emailadress',$_COOKIE['emailadress'],PDO::PARAM_STR);$unsubscribe->execute();

TO GENERATE A LINK, you can do it like this and send it to the persons emailadres:

$length = rand(5, 10);$link= "";for($i=0;$i< $length;$i++)/*create random link*/{   $char = rand(0, 256);   if(($char>=65 && $char<=90) || ($char>=97 && $char<=122) || ($char>=48 && $char<=57))   {      $char = chr($char);      $link.= $link;   }   else    $i--;}$hash =  hash("ripemd160",$link);setcookie('unsubscribe',$hash,time()+300);$result = mail($emailadress, 'unsubscribe link', 'you are about to unsubscribe yourself. Click this link to unsubscribe: http://yourSite.php?link='.$link);

And in this page, you can use the code to delete the subscriber as mentioned above.

PS: the link itself shouldn't be add to the database because you can set a cookie which is valid for a certain amount of time (here this is 5 minutes).in the page this page you can then add an if-test to see if the cookie was set and then delete the subscriber. if(isset($_COOKIE['unsubscribe'])){...}

Hope it helped ;)