SImple really...
- IOS9 introduced a bug which has completely screwed up the manner in which Mail is handled for many users. Some people choose to use a protocol known as POP3, this is what's screwed up for many people. Apple actually use another protocol known as IMAP, some people report issues with this also, but there are far fewer reports of issues.
- Subsequent IOS releases have failed to rectify the problem.
- Apple devotees have gone from initially denying there was any issue, to admitting there is an issue.
- Apple have failed to acknowledge the issue or provide any indication as to when it will be fixed.
- Some users playing with Beta software have stated the issue is no longer present, but as Apple prohibits any discussion regarding Beta s/w, these posts are in the main quickly deleted. (Despite Apple not being here)
- Many of Apples customers are well and truly fedup.
If you want reliable email, then best to avoid IOS9 for now.