(PHP 5, PHP 7 >= 5.3.0)
imap_gc — Clears IMAP cache
$imap_stream
   , int $caches
   )Purges the cache of entries of a specific type.
imap_streamAn IMAP stream returned by imap_open().
caches
       Specifies the cache to purge. It may one or a combination
       of the following constants: 
       IMAP_GC_ELT (message cache elements), 
       IMAP_GC_ENV (enveloppe and bodies),
       IMAP_GC_TEXTS (texts).
      
  Returns TRUE on success or FALSE on failure.
  
Example #1 imap_gc() example
<?php
$mbox = imap_open("{imap.example.org:143}", "username", "password");
imap_gc($mbox, IMAP_GC_ELT);
?>