I thought I had a new idea, but after a quick search I found this feature already requested (and implemented) on the cPanel forum:
My idea shares much of that thread, but I wrote all this before I found that thread so I'll continue...
Since it's the domain administrator and not the end-user who creates mailboxes one of the first things the user needs to do (and should do) is go to the webmail to change their password. If the user likes the webmail experience - great, they can continue on and nothing needs to happen.
However, if the user insists upon using their familiar email client, then I think there should be a page somewhere within the webmail (ie after they've logged in and set / changed their password) which has very specific instructions on how to add their account to a variety of the most popular email clients.
In particular, for iOS users, that page should have a button they can click which generates their personal .mobileconfig file, and opens it on their device to add the mail account. It would be easy for the webmail page to even detect that the user is on an iOS device and only show the button if that's the case. As far as I know, the only way to autoconfigure a mail account on iOS is via a .mobileconfig file.
By having this type of instructions page available within the webmail it allows the instructions on that page to be extremely specific because the user is already logged in, and the webmail should know the exact settings required in order to access that specific user's account via other protocols. Ideally, if the autodiscover.xml file works properly most of the other major email clients should be able to use that, but if not, and the user is configuring things manually, the more specific the instructions the better.
Having SmarterTools do this once and maintain it as part of their core webmail client is probably much easier than having thousands of system administrators like myself trying to come up with our own instructions. And again, having it available only within the webmail ensures that the user 1) logs in to set/ change their password as their very first important step, and 2) exposes the user to the webmail interface which hopefully influences them to at least give it a try and perhaps use that instead of their normal mail client.