With regard to accessing attachments contained in deleted mail files check to see if the email(s) are still in the trash folder. If so it can be restored and the attachment accessed.
Firstly,make sure to move the emails with big sizes by either deleting them or archiving them
secondly, compact your database because there must be a withe space in your database and in order to do it do the following :
– select the second tab “Info”
-click “compact “