Outlook 365 external access Exchange 2019 and password prompt

Hey all,

Some info:

Exchange 2019 all on-prem (no hybrid)

Windows 10 with Outlook 365

When a domain joined pc connects to an external network, after the user logs into the pc (we permit one set of credentials to be cached) Outlook requires the user to enter their password.

Is this normal behaviour, or is there a setting to allow Outlook to connect from externally using the logged in credentials?

thanks

jc

EDIT: can anyone advise the implications of enabling Windows Authentication on owa on the default site?