Bertel King, Jr. is an independent novelist and freelance writer living in the beautiful mountainside of Pittsburgh, Pennsylvania, where he makes worlds come alive using free software. You can follow his work at bertelking.com.
In your Gmail, all you have to do is to enter the term size:10mb in the search box and all emails larger than 10MB will show up in the list. You can change the number to reflect the size you want to filter.
This is so far the easiest way to filter your emails by size.