iOS Outlook app allows Microsoft to see all mail account and server credentials without the users knowledge.
He elaborates thisin detail here.
Also the iOS Outlook apps built-in connectors to OneDrive, Dropbox and Google Drive are a data security nightmare.
If you decide to sign up to use the service, you will need to create an account.
That requires that you provide the email address(es) that you want to access with our service.
Untill the security issues can be resolved.
source: www.techworm.net
