If Postie isn't working right and you see "Fatal error: Out of memory..." in your logs it is time to increase how much memory PHP allocates to WordPress.
By default 40Mb is allocated.
To change your memory open up your wp-config.php file and add one of the following settings
Increase PHP Memory to 64MB
define('WP_MEMORY_LIMIT', '64M');
Increase PHP Memory to 96MB
define('WP_MEMORY_LIMIT', '96M');
Please note, this setting may not work if your host does not allow for increasing the PHP memory limit--in that event, contact your host to increase the PHP memory limit. Also, note that many hosts set the PHP limit at 8MB.