I've been working on a nice feature for my local classified ad site which involved
retrieving emails (IMAP account) and analyzing the content.

What I wanted is when I am done with an email to move it in a folder so I don't have to reprocess it again.
Sounds easy and it should be that way.

For some reason when you delete OR move messages, their ID changes as well. It could be a Zend Framework thing. So I had to collect the unique IDs in the first loop then use a second loop to move the messages.

I decided to move the messages rather than deleting them because I am using Google Mail for my domain and there is plenty of space.
If I ever need more space I can always order more.

Note: in my code below the messages are moved in '[Gmail]/All Mail' which of course is fine for Google hosted emails, you've got to change it depending on your IMAP setup.

Here is the code

try {
            $imap = new Zend_Mail_Storage_Imap ( array (
                 'host' => 'imap.gmail.com:993',
                 'user' => 'your@gmail.com',
                 'password' => 'yourpwd',
                 'ssl' => true
            ));
            
            echo $imap->countMessages () . " messages found.\n";
            
            $uniq_ids = array ();
            
            foreach ( $imap as $idx => $message ) {            
                $messageUniqueId = $messageId = $imap->getUniqueId ( $idx );
                $uniq_ids [] = $messageUniqueId;                
                
                echo "[IDX: $idx UID: $messageUniqueId] Mail from '" 
                    . htmlentities ( $message->from, ENT_QUOTES, 'UTF-8' ) . "':  to '" 
                    . htmlentities ( $message->to, ENT_QUOTES, 'UTF-8' ) . "': {$message->subject}\n<br/>";

                echo '<pre>';
                echo $message->getContent();
                echo '</pre><br/>';
                
                if ($idx && ($idx % 5 == 0)) {
                    $imap->noop (); // keep alive
                }
            }
            
            // I will assume that the messages are processed so move 'em in All mail. I hope that's the archive.
            // Note your Folder may be differently.
            $cnt = 0;
            foreach ( $uniq_ids as $uniq_id ) {
                $cnt ++;
                
                if ($cnt % 5 == 0) {
                    $imap->noop (); // keep alive
                }
                
                $messageId = $imap->getNumberByUniqueId ( $uniq_id );
                $imap->moveMessage ( $messageId, '[Gmail]/All Mail' ); // this ID shifts all the time (--1) ?!?
            }
        } catch ( Exception $e ) {
            echo '' . $e;
            Zend_Debug::dump($e);
        }