Maybe you did not notice but as of last week Google has added two new search options for users of Google Apps and Gmail. These two options allow you to clean up your email box and keep it in the limit very quickly.
larger:10m – look up inside of entire email box all messages that are bigger than 10MB and it is not about the attachment as it was before. This is searching for the email message regardless if there is or not attachment that is in size over 10MB.
older_than:1y – look up all messages in your email box that are older than 12 months and you can decide if you still want to keep them and archive or delete from your email box.
You can even combine both options together in search:
This means, for example, to find emails larger than 5MB, you can search for size:5m or larger:5m or to find emails sent over a year ago, older_than:1y. Her you can find more on advanced search options that you can use while using Gmail or Google Apps email. = Using Advanced Search