If you notice that you're program's memory usage is increasing (as observed using ps) while calling the imap functions, calling this function should free that memory.
    (PHP 5 >= 5.3.0, PHP 7)
imap_gc — Clears IMAP cache
$imap_stream
   , int $caches
   ) : boolPurges the cache of entries of a specific type.
imap_stream由 imap_open() 返回的 IMAP 流。
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 (envelope and bodies),
       IMAP_GC_TEXTS (texts).
      
  成功时返回 TRUE, 或者在失败时返回 FALSE。
  
Example #1 imap_gc() example
<?php
$mbox = imap_open("{imap.example.org:143}", "username", "password");
imap_gc($mbox, IMAP_GC_ELT);
?>
If you notice that you're program's memory usage is increasing (as observed using ps) while calling the imap functions, calling this function should free that memory.