Gmail and Outlook already contain a subscription ledger: almost every paid app sends a receipt. The problem is volume. Those receipts sit under newsletters, shipping mail, and two-factor codes. You can search by hand, or let Unwanted Subscription scan with read-only OAuth so you never type a mailbox password into the app.
What to search if you do it yourself
In Gmail, try:
subject:(receipt OR invoice OR subscription OR membership) newer_than:365dfrom:(netflix.com OR spotify.com OR adobe.com OR apple.com)
In Outlook, use the same words in Search. Filter by Has attachments if your bank only sends PDF invoices. This is slow, and it still misses merchants that never say “subscription” in the subject.
What Unwanted Subscription reads
When you tap Continue with Gmail or Outlook, you sign in with Google or Microsoft. That is OAuth. We never see your mailbox password. The permission is read-only: no send, no delete, no filter changes.
The server looks at likely receipts and billing mail (App Store, Google Play, and known merchant domains), extracts merchant, amount, and date, and returns a list to the app. Message bodies are not stored. What we keep so a later scan can run: the inbox email address, OAuth tokens, and scan status. Disconnect the inbox and those go away. Full write-up: Privacy Policy.
What an inbox scan cannot see
iCloud Mail is not offered. Apple does not allow third-party apps to OAuth into it. Cash gyms, some VPNs, and charges that only hit the card still need a statement.
It can also over-match: a one-time Adobe license email is not Creative Cloud. Treat the list as a starting point. Open the merchant or the statement before you cancel.
After the scan
You will see a monthly total first. Names unlock with Pro. Then you keep or cancel. Guides for the usual stack:
If you only wanted a second opinion on Gmail, you can disconnect as soon as the list is on the phone. The list stays local.