Here's an example of attachment from Google Drive:
If you pick a file that's too big, you'll get this error message: "Your message could not be saved because it exceeds the maximum size of 25 MB. Try removing an attachment."
"There are now more ways to share Drive files with friends and family through Gmail, without having to worry about accidentally removing their access. By selecting the 'Insert as Attachment' option from Drive you'll be able to attach non-Google files directly to your Gmail message. Now you can be sure your friend will always have that great candid photo from your weekend getaway, or the PDF for your aunt's fruitcake recipe (do people actually eat Fruitcake?) even if you delete it from your Drive," informs Google.