This is an issue I've had I think ever since iCloud was released some 4 years ago now, but as I'm no closer than I was then to solving it, I'll put it out here on my blog, and see if others may have ideas. Part of a user's iCloud storage is used for their iCloud email account, should they wish to make use of it. I do use my iCloud email account, though not all that often. Currently, when I check to see how much storage various things in iCloud are taking up, most make sense, except for mail. Let me explain. My iPhone backup currently takes up about 609 megabytes of space, which sounds about right, since I do have several voice memos, and various other audio apps that I keep data backed up in iCloud. Plus, I believe iCloud keeps the most recent 2 backups I think it is, so all that data added up would come out to the figure I mentioned above. The mail portion of my iCloud storage though makes no sense whatsoever. At the moment, my iCloud mail contains a total of 4 messages, 3 of which are normal simple plain text emails, that should only be a few kilobytes each. The 4th message does have 2 .xml files attached to it, as well as a plain text description of what the attachment of the message contains. The attachments in all total around 50KB in size. I'd estimate that all my iCloud mail combined should take up maybe 100-300KB total, when you factor in header information, along with the message overhead for the attachments. There's no way for me to see the exact size of the individual messages themselves to be sure, so I'm just estimating based on the message contents. So, if my total iCloud email size is let's say 300 kilobytes, then why does it say that mail is taking up 10.7 megabytes of my iCloud storage! Yes you read that right, with nothing at all in my junk or trash folders, or my sent folder, the 4 messages I have stored in iCloud which are quite small themselves, are somehow taking up a crazy 10.7MB of my space! A while back, I tried to dig into this issue, back when my iCloud settings showed that my mail portion of storage was using an insane 147MB of space. I primarily use my iCloud account on my phone, but when I cleared out all messages from there with no noticeable change, I brought up mail on my mac, and cleared out stuff from there and that did seem to help, as my mail was then only using a few kilobytes of space. I also discovered that notes that you create with the notes app are actually stored in the mail portion of your iCloud storage. This may be different now with iOS9, though I haven't yet tested to be sure of that. Anyway, with no mail at all in iCloud, and with the only thing taking up the mail portion of my storage being my notes from my notes app, the size of mail storage used looked right, at about 90 kilobytes or so. I then sent myself a simple test plain text email, which even with header information and all should be just a few kilobytes in size, and after receiving the message, I was shocked when I looked at how much iCloud mail was taking up, and it had jumped from 90KB, to over 5 MB! Remember that I had not sent myself any attachments whatsoever. I'd literally sent just 1 message with a subject of testing and body of "this is a test message." There's no way in hell that message alone, even with header information and such, would've been 5 megabytes by itself! That message couldn't've traveled through so many mail servers, so as to make the header info of the message 4 or 5 megabytes! I did then send myself a message with an attachment of around 1.5 megabytes, and the storage used after receiving that message jumped up to over 10MB. The message itself again including all headers should have been less than 5MB. I still have no explanation as to why mail storage space is so way off the mark. And as I said, at this very moment, I have 1 message that contains 2 small attachments, and 3 other plain text emails, and my mail storage should not even be close to 5 megabytes, let alone the 10.7 megabytes that it's showing right now! Does anyone have any idea what on Earth is going on with this? I'm not running out of storage or anything, I'm just curious why mail storage seems to store more data then should be there, and what that data could be. It'd be like me withdrawing $60 at an ATM, only to discover my account showing I withdrew $120, even though I know for a fact I've got 60! Strange stuff, and if anyone has ideas, I'll take them.