Almost 6 years after it was introduced, you still can't attach files to emails in iOS. While iOS 6 has introduced a method to attach photos and videos to in-progress emails, it suffers from poor discoverability, and only works with content from the Photos app. If you want to attach any other file to an email, it's a usability disaster.
Adding photo or video attachments to in-progress emails is done via the same pop-up menu originally introduced in IOS 3 for cut, copy, and paste. You have to tap the screen to get the popup, tap a tiny, obscure arrow button to get more options, and then tap to add the attachment.
An easy to find, easy to use attachment button would be simpler. It's a solution employed by third-party apps like Facebook, email clients like Gmail and Sparrow, and the official Twitter app and Tweetbot.
Some of these are more elegant than others, but all of them are more discoverable. And that's still only for photos and videos. What about files?
Emailing, and including files as attachments in email, is a common task and something that takes only a few seconds on the Mac with OS X. Trying to attach a non-photo or video file on an iPhone or iPad with iOS takes an annoying amount of time and causes an unreasonable amount of frustration. Here's some blog-theater by way of example:
"Hey, Rene, can you email me the dates for that trip?"
"Sure, Kevin." I grab my iPhone, open the Mail app, add Kevin as the recipient, add the subject "trip", paste in the dates, then--
"Could you also attach that outline for discussion topics?"
My only option now is to copy the contents of the email, trash it, go to the app I wrote the topics in, find the file, tap share, tap email, add Kevin again, add the subject again, paste in the dates again--
Shit. I deleted the app I wrote the topics in. A hotter, newer app came out and I started using that instead, and even though both use iCloud, neither has any idea the other exists so... I re-download the old app and pray the data is either still there, or magically comes back from the cloud.
"And those two PDF files about that thing?"
Double shit. Both those PDF files are in different PDF apps, one in a simple reader, the other one in an app that supports annotation. Now I have to send the discussion topics from one app, and each of the PDF files from their apps. That's three separate emails, and nothing approaching a thread.
Now Kevin is laughing his ass off at me and asking me to tell him again how the iPhone is easy to use, and I want to punch things.
And the reason for all this is that Apple forgot a cardinal principle of design: unreasonable simplicity sometimes leads to inane levels of complexity.
Apple already uses a blue + button to add contacts. Something like that could work for attachments as well. (I did a mockup along those lines for a pre-iOS 6 article on higher hanging fruit, but I'll update it below.)Tapping the attachment button could bring up a Share Sheet that includes the Photos icon, so you could attach photos as normal, but also any other app icon that contains documents. Tapping an icon would bring up a list view of all the files associated with that app. It's a bit overwrought, but it fits with the existing iOS constructs, including the binding of files to apps, and has the advantage of familiarity-as-a-feature.
Depending on how many file-capable apps are installed, it could create a very dense Share Sheet. It also still requires the user remember which app contains which file.
That's why, for the last couple of years, I've been asking for a simple, flat document repository for iOS -- a Files app that works the same way as the Photos app (or Passbook app for that matter). A Files app for iOS would remove unnecessary cognitive load from users and solve a wide swathe of current usability problems with iOS, including email attachments.
With a document repository, any user file could be attached to any in-progress email, without the need for a Share Sheet, or for the user to remember app ownership. And it would do so in a way that's consistent with how iOS already works, increasing simplicity at the same time.