Pay attention to the suggested sharing resolution on iOS when you share a picture using “Mail”. Its common for mail apps to downscale images to make them lighter to send.
If you wish to share a photo in HD (best possible quality) be sure to select “Actual size” when sending your mail. Be sure to scroll down on the proposed resolution list – this option is usually the last entry.
WARNING: some applications don’t allow you to chose the resolution (Like Whatsapp) and will automatically downscale your images – be aware of this if you want to share the best resolution of your images.
If you want to get all your HD files in once we strongly recommend you do it on your web account