Fatal error when I export emails

Hi,

For some reason when I try to export my emails from my subscribers im getting this “Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 72 bytes) in /home/freedrumkits/public_html/wp-includes/wp-db.php on line 1780” and I cant download my emails, I called my hosting company and they said everything is fine server wise, I also went in my wp-config.php page and upped my memory and still having this problem, it just started doing this please help!!!