It's a question as old as iTunes itself, and one we’ve been asked about a couple of time here at Legitmix as people search for a forgotten remix needed for a class or competition. The simple answer is that while you can play back an MP3 you've emailed yourself, you can't add it to your iPhone's music library. Click on an MP3 you've attached to an email on an Apple device and it will playback for you using a surprisingly responsive little player. After you’ve listened to it once you can even come back and play it again later while not connected to the internet. If you want to add the MP3 to your device's iTunes library though, you'll still need to plug in to your desktop computer and do it the old fashioned way.
So why is it, in the world of delivery drones and electric cars that you can’t add an MP3 to your iTunes library through email? Well, that goes back to the very earliest version of iTunes. Way back in 2003, when Steve Jobs was first negotiating with the major music labels to get their catalogs up on iTunes, digital music sales weren’t exactly mainstream and the record industry was still reeling from the piracy floodgates being opened by Napster. Limiting the ability of users to add songs to their iTunes via email was likely one of the concessions made by Apple to help persuade the labels to come on board. It may not have even seemed very relevant at the time, since iTunes was only available on a few Motorola phones and the first iPhone was still four years away.