The only mail-on-device Ive found
This is the only app I have found which keeps the mail actually on my device.
All other iOS mail apps are only reading the mail that is available online. Offline mail lets me read my long history of email for as far back as I have been using it and uploading from other services. For example I have mail back to 2006 offloaded from one of my Hotmail accounts. From my 12 email accounts I have over 50,000 emails on my device device. It is also the only way I can rapidly search the entire history of my emails without an online connection. It also seems to fetch recent emails faster than Apple Mail.
I cant give it five stars because it does not have a mark all feature, for example to mark selected or all as read.
dgd3 about
Offline Mail - your email offline with fast search, v8.4.1