Re: Outlook email contacts
There is no such thing to Aqua Mail.
Mail apps don't talk to each other, don't know about each others' existence, and don't magically pull contacts from each other.
I assume you meant "Outlook the Windows app" here, BTW.
Re: preventing 3-rd party apk such as Aquamail from reading Outlook.pst files
It never did and probably never will "read Outlook .pst files".
For accounts set up as Exchange type, Aqua Mail can auto-complete and access email addresses from the server address book.
For other account types, Aqua Mail auto-completes from Android Contacts (People) "app". How they get their is mostly not its business.
And two cherries on top:
1 - Aqua Mail can also search a certain number of your actual recent messages (stored on the device) and offer email addresses from there, even if they're not stored anywhere.
App settings -> contacts -> recent addresses.
2 - Aqua Mail can collect and save addresses from the messages you send
App settings -> contacts -> auto-save
These addresses are saved into a separate group called AquaMail.