Why is Google sign-in invite-only?

Google fully verifies apps that read Gmail only after a paid, independent security assessment. BLAM8 is self-funded and is completing that assessment once its first founding customers are aboard rather than before — we'd rather be honest about the order of operations than pretend otherwise. Until it completes, Google limits how many people can sign in to BLAM8 with Google and shows an "unverified app" notice on its consent screen, so Google sign-in is invite-only and the limited places are saved for founding users. The login page shows exactly how many places remain; Microsoft sign-in has no cap and is open to everyone.

None of this changes what BLAM8 can access. Consent still happens on Google's own screen, scoped to the mailbox and calendar you choose, revocable from your Google account at any time — and draft-only by default applies exactly as everywhere else. When you connect a Gmail mailbox you may see "Google hasn't verified this app": continuing via the Advanced link is Google's standard route for apps at this stage. If you'd rather not, Microsoft 365 / Outlook works identically, with no notice and no cap.