Use iCloud to send large files
Mail in OS X will only send attachments of less than 40MB, so if you spend a lot of time uploading large files onto sharing services like Dropbox and pasting links into your emails instead of the files themselves, then you'll want to use the Mail Drop feature (only found in Yosemite’s version of Mail) to send attachments.
The first time you attach a large file to a message you’ll get a warning that you’ve exceeded the maximum size. If the file is an image you can slim it down using the Image Size control in the composition window, but this degrades the image’s quality.
So, rather than shrinking an image, ignore the warning and click Send. Mail will display options that include a Mail Drop button. Click that and so long as the attachment is 5GB or less it will be removed from the message and uploaded to iCloud – though you won’t actually see it in Drive because it’s not stored there and doesn’t count against its storage limit. It will be available to download for 30 days. Although Mail Drop doesn’t affect your storage quota, it is subject to a total 1TB limit in any 30-day period. Apple mentions some other limits at http://apple.co/1TD9fkw.