Mail Drop is an incredibly useful tool when emailing large attachments with the Mail app in OS X. It kicks in when you attempt to send an attachment larger than 20MB (and up to 5GB) and uploads the file to iCloud, where it'll sit for up to 30 days for your recipient to download at his or her convenience.
If you have frequent recipients whose email provider has a lower limit for attachments than 20MB, then some of your emails may fail to send. Thanks to this post on OS X Daily, I found a simple Terminal command to change the minimum threshold for Mail Drop.
Open Terminal, enter this command, and hit Enter:
defaults write com.apple.mail minSizeKB 10000
In this example, Mail Drop will offer to upload attachments larger than 10MB.
Restart Mail and the new setting will take effect. You will also need to be running OS X 10.10 or later with iCloud enabled.
In other email attachment news, the Dropbox for Gmail Chrome extension hasto make it easier to send and receive large attachments.