Please keep in mind that email is not an ideal file transfer method. Emails with large attachments consume unnecessary amounts of mail server resources. There are better ways to transfer large files.
Every mail server has different maximum attachment sizes that they allow. Rackspace email currently allows 50MB files, and Gmail (Google Apps) allows 25MB. But keep in mind just because you can send a large file, the other person may not be able to receive it.
We recommend you don't send files larger than 10MB in a single email.
If you need to share large files, you can upload a file to your Gutensite Website Document Library (limit access to one account if it's private). You can also use Google Docs, Dropbox, or other services. Do a search for "Send Large File".