The solution is to update your SMTP plugin. Try WP Mail SMTP: https://www.ads-software.com/plugins/wp-mail-smtp/. It has many more options than WP SMTP and also has built in diagnostics.
And just for the record, some web hosts (example: Bluehost) do block outgoing SMTP connections from their servers to servers not within their control but this Office 365 SMTP issue is pretty common and effects all older apps/plugins that use SMTP because their implementation of TLS is either not compatible with Office 365 or they simply do not have TLS as an option. Other than that, the protection tab does not block connections by default so don’t even bother looking there.
Hope that helps!
