This will likely roll up into another blog post, but writing it down so I don't lose it.
In the 2000's using a computer meant using the windows desktop. Two common capabilities from those days were the ability to do a user initiated share of data between applications, and the ability to asynchronously notify the user.
User initiated data sharing on the windows desktop was accomplished with drag and drop. Today there are no apps so there is no notion of sharing between them, except - e-mail. For example, if you want to share a video via youtube, you can send a mail to a special youtube address.
Asyncronous user notification used to be done with notification windows in the bottom user of your screen. Today there is no notion of an on your latest device alerting platform - except e-mail. For example if youtube wants to tell you your video is ready to be shared, you get an email.
Cool how the world evolves eh?