Rythm filters email with two user-controlled layers. Layer 1 is identity: Rythm builds a guest list of people you already know from your contacts, sent folder, starred messages, and inbox frequency. Layer 2 is cost: anyone not on the guest list sees a polite rejection notice with a link to pay a small cover charge (default about four cents). Known senders walk in; unknown senders either pay or get held for review.

Does Rythm work with Gmail?

Yes, any Gmail or Google Workspace account. Connect via Google OAuth.

Does Rythm work with Outlook?

Yes, any Outlook or Microsoft 365 account. Connect via Microsoft OAuth.

How long does onboarding actually take?

Around 12 minutes end-to-end: 10 seconds for OAuth, 8–10 minutes for the guest list scan, a minute or two to pick your cover charge and wallet.

What Lightning wallets are supported?

Any LNURL-compatible wallet. We recommend Cash App, Strike, Blink, Primal, or Tether Wallet; most take 2 to 10 minutes to set up.

What happens if I miss something important in RYTHM: REJECTED?

Nothing is deleted. The folder is a waiting room. Drag an email back to your inbox and that sender is added to your guest list for good.

What happens when I cancel?

Rythm stops processing your email, the labels can be removed automatically, and your inbox returns to exactly how it was. No lock-in, no lingering changes.

How does the guest list get built?

Rythm runs a four-phase scan on connect: starred/flagged messages (people you explicitly value), your contacts book, the sent folder (anyone you have ever emailed), and inbox frequency (anyone who emails you regularly). Total time: about 8 to 10 minutes. After that, the guest list maintains itself; rescue from REJECTED once and the sender is added forever.

What happens to unknown senders?

They receive a short, polite rejection notice (the copy is customizable from the recipient's dashboard) explaining that the recipient uses Rythm and including a one-tap link to pay the cover charge. The cover charge amount is set by the recipient. If they pay, the email is delivered labeled RYTHM: PAID and the payment settles to the recipient's wallet. If they ignore it, the email stays in the RYTHM: REJECTED folder, which is a quarantine the recipient can rescue from in one click, not a trash can.

What is Cashu and why does Rythm use it?

Cashu is an open ecash protocol built on top of the Lightning Network. It lets a sender pay once and attach a cryptographic payment proof that the recipient can redeem directly, without Rythm ever holding the money. This is what makes Rythm non-custodial by design.

Rythm is a dual-layer deterministic email filter for Gmail and Outlook. Known senders walk in with no extra cost; unknown senders pay a small cover charge (default about four cents) that settles directly to your wallet. Non-custodial by design, powered by the Cashu ecash protocol over the Lightning Network.

Is Rythm non-custodial?

Yes. Rythm never stores your email content and never holds your funds. Cashu tokens are validated in-memory for milliseconds, then discarded. Payments flow from sender, to a public Cashu mint, to your Lightning wallet.

Does Rythm try to detect AI-generated email?

No. Rythm is a bouncer, not a lie detector. The cover charge creates intention: a sender who paid $0.04 has signaled that reaching you was worth it, whether a human or AI wrote the text. Rythm filters on intention, not content.

How Rythm Works: A Dual-Layer Deterministic Email Filter

two layers

Identity, then cost.

Two questions at the door. Both binary. No probability score, no machine-learning guess.

layer 1

The guest list.

Your guest list is the list of people who reach your inbox at no extra cost. You don’t build it. You don’t maintain it. It just works.

Initialization. When you connect your inbox, Rythm auto-builds your guest list in about 10 minutes by scanning your existing email. Anyone you’ve corresponded with, starred, or saved as a contact is in.

Ongoing. From then on, the list keeps itself fresh based on how you use email. Reply to a new sender, star a thread, or drag a message back from the waiting room, and they’re added automatically. No tagging, no manual approval, no list management.

You can see the entire list. You can edit it. You can rescue anyone. The list is yours.

layer 2

The cover charge.

Anyone not on your guest list sees a rejection notice with a link: here’s how to reach this person’s inbox, a small cover charge. You set the amount. As low as a couple cents, or higher if you want. The default is around four cents.

The math is the point. At four cents, a real person with a real reason to reach you won’t blink. At spam scale, it’s catastrophic: a campaign of 100,000 emails would cost $4,000 out of pocket. Any cost at all destroys mass outreach economics, because mass outreach only works when it’s free.

Paid emails are delivered to your inbox with the label RYTHM: PAID. Unpaid emails from unknowns are moved to the RYTHM: REJECTED folder. Nothing is deleted. Think of it as a waiting room.

On top of your guest list, Rythm maintains a small managed list of high-importance, low-velocity domains (a handful of major banks, court systems, the IRS, shipping carriers). Mail from those specific domains lands in your inbox without a cover charge, with DKIM verification on each message to guard against spoofing. This is a short curated list, not a blanket pass-through for every transactional or 2FA email. Codes from a service you’ve already used reach you because that service is on your guest list. Codes from a brand-new service may hit the cover charge the first time, which is rescuable in one click.

setup

Three steps. About 12 minutes.

One sign-in, one auto-scan, one cover charge. The bouncer is on shift before you finish your second coffee.

Connect your inbox.

Sign in with Google or Microsoft OAuth. Rythm requests only the minimum permissions needed to scan incoming unknown-sender messages for payment proofs and apply labels (Gmail: gmail.modify; Microsoft: Mail.ReadWrite). Rythm doesn’t send mail from your account; rejection notices come from Rythm’s own notification address. Your email content is never stored on our side. Takes about 10 seconds.

Your guest list builds itself.

Rythm scans starred/flagged emails, contacts, sent folder, and inbox frequency to auto-build your guest list. The four-phase scan runs in the background and typically finishes in 8 to 10 minutes. When it’s done, everyone you already know keeps reaching your inbox with no friction.

Mass outreach only works when it’s free.

Why a four-cent door charge changes everything.

Set your cover charge.

Pick the amount unknown senders pay to reach you. Default is ~$0.04, trivial for a real person, catastrophic at spam scale. Connect a wallet (Cash App, Strike, Blink, Primal, or Tether Wallet). The money lands in your wallet in seconds.

under the hood

The plumbing.

When an unknown sender pays, a small payment proof rides along with the email. Rythm checks for it, confirms the payment, and the money lands in your wallet in seconds. We never hold it and we never store your email content. The scan happens in memory and everything else is discarded.

For the technically curious: Rythm uses the Cashu ecash protocol over the Lightning Network to move the sender’s payment directly to your wallet. If anything breaks on our end, your email still delivers normally.

Rythm is email processing software. It is not a cryptocurrency service, payment processor, money transmitter, or custodian of funds or tokens.

How Rythm works: the bouncer, the guest list, and the cover charge.