Create a new search list based on the following parameters and delete all the mails
To Delete old Mails : Before certain date
1. In the search option i.e. "Has the words" field, type before:2010/01/23.
2. That's just an example date; it would delete all messages received prior to January 23 of year 2010.
3. You can use any date you want, as long as it conforms to the format YYYY/MM/DD.
Find the Large Attachments
1. In the search folder type size: 5000000, this is size greater than 5MB