Right now we do not have any tests to test whether we can actually sync with various popular services, from regular IMAP servers, to GMail, iCloud, Office365, Yahoo etc., including contacts and calendars.

I would propose to create accounts on all those services with credentials available to all core KDE PIM developers (so the accounts cannot be abused for spam etc.), and develop, probably as a completely stand-alone project, a complex integration test that would set up each account in Kontact and verify it is synced correctly.

Finally, we should talk to sysadmin if it would be possible to have the test executed as a standalone job on the CI on some regular basis (nightly?) against current PIM installation.