Mail Drop offloads big OS X Mail file enclosures to iCloud.

Mail Drop was introduced in 2014 with the release of OS X Yosemite. It makes it possible to attach file enclosures up to 5 GB in size to your email without gumming up your email server. OS X and iCloud handle it behind the scenes automagically. Since many employers and service providers strictly limit how big email file enclosures can be, Mail Drop makes it easy to send big files without having to worry that they'll actually get there.

The way Mail Drop works is invisible on OS X and iOS: Your recipients see the file attached, even if it's sent via Mail Drop. Users of Windows and other operating systems will see a link to download the file.

By default, Mail Drop kicks in if you try to attach files to your mail message that are 20 MB or larger. Some organizations have even more draconian limits on the allowable size of email file attachments. They may impose limits of 10 MB or less.

There is a way of changing the default trigger for OS X to invoke Mail Drop, however. You can do it from the command line in the Terminal utility.

In this example, I'm going to reset Mail Drop's threshold from 20 MB to 10 MB. You can change that value to whatever you'd like, however.

Bear in mind that Mail Drop does have some limitations: Enclosures can be a maximum of 5 GB, and Apple imposes a 1 TB storage limit. Each file enclosure automatically expires after 30 days.

How to adjust OS X's Mail Drop threshold

  1. Open Terminal.
  2. Type defaults write minSizeKB 10000. (You can copy and paste that text into the Terminal app command line if you prefer.)
  3. Hit return.
  4. Quit Terminal.

Have any questions? Let me know.