The Disk cache is enabled by default, provided sys_get_temp_dir() exists. Using disk caching provides speed improvements when sending large attachments and it provides a consistent level of memory use (roughly 1.68 MiB).

To explicitly use disk caching place these lines anywhere before you send any messages. There is no need to use this code in the same script multiple times; only call it once.

<?php
 
Swift_Preferences::getInstance()->setCacheType('disk')->setTempDir('/tmp');

Where “/tmp” is replaced with whatever writable directory exists on your server.