Fromboxes

What is a frombox

A frombox is an on-chain account for one (sender “from” address, recipient “to” wallet) pair. It holds a prepaid balance of “stamps” and the postage price of a single stamp — sending one email always costs exactly one stamp, so this is the per-email price for that particular sender writing to that particular recipient. Where a mailbox is 1:1 with a recipient, a frombox is 1:1 with a specific sender-recipient relationship — the same mailbox owner can have a different frombox (and a different stamp price) for every sender who writes to them.

Every GUI client’s Balances pane shows your fromboxes’ prices and stamp balances — see the webmail, Chrome, or Outlook client pages.¹

Default postage and pricing

New, never-before-seen senders don’t have a frombox at all: the recipient’s mailbox default postage (also a per-stamp price) applies instead, and that default is normally set high specifically to price out spam from unknown senders. Once a recipient knows and trusts a sender, they create a frombox for that sender and set a lower, negotiated stamp price.

The default is not entirely one-size-fits-all, though: a sender wallet with a real on-chain track record — cumulative postage spent reaching other recipients, or a verified-sender attestation from its domain — pays a scaled share of the default at first contact, down to a tuned floor. Spam economics are unchanged (a burner wallet has no record and pays full price), and a price the recipient sets is never scaled — see Reputation-scaled first-contact pricing.

The anti-spam lever

A frombox’s per-stamp price — the required_postage a sender pays for each email — is the recipient’s core lever against spam and phishing alike: a price is content-blind, so there is nothing for a better-written forgery to get past. A freshly created frombox inherits the recipient’s mailbox’s high default price (1 SOL on a new mailbox — a wall, not a going rate), and the recipient can drop it for a sender they trust, or raise it — even above the mailbox’s own default — for one who has become a nuisance. Friends are free: when the recipient funds a correspondent’s frombox themselves, the per-stamp protocol fee is waived and the value round-trips back as that correspondent’s mail arrives.

Only the recipient can change this price: the update must be signed by the recipient (“to”) keypair, and the on-chain program checks that signer against the mailbox owner, so a sender can never discount their own postage.

That same ownership underpins an owner exception: normally opening a brand-new, empty frombox with zero stamps is refused (see the prepayment rule below), but the recipient may set a price for a sender’s frombox before that frombox — or any purchase from the sender — exists at all. Because the signer setting the price is the mailbox owner, the on-chain guard allows this one stampless create; a third party can never open an empty frombox this way. The frombox starts at the recipient’s chosen price with zero stamps, so the sender still can’t reach them until it holds at least one stamp, funded by either side.

Reprice a sender from your client’s Balances pane — see the webmail or Outlook client pages.²

Prepaying with stamps

Stamps are the currency of delivery: sending one email always burns exactly one stamp, so a frombox with no stamps left can’t receive mail from that sender until it is topped up. Buying stamps prepays postage into a frombox, creating the frombox on the spot if it does not exist yet: a newly created frombox always inherits the recipient’s mailbox’s current default postage as its per-stamp price — the deliberately high value that prices out spam. Buying stamps never sets a custom price on its own; giving a trusted sender a cheaper rate is a separate step, done either afterwards or up front, as described in the anti-spam lever above.

This first-purchase behavior is bounded by the prepayment rule: a third party — a sender funding their own frombox to someone else, or anyone other than the recipient — must buy at least one stamp on that first purchase. An on-chain guard refuses a zero-stamp create from a non-owner payer, so a spammer cannot litter the chain with empty fromboxes for free — for anyone but the recipient, opening one always costs at least one stamp of postage. The only way to open a stampless frombox is for the recipient to do it while setting the price, as described above.

Buy stamps from your client’s postage form — the webmail Balances pane, the compose card’s inline prepay when a send is refused for stamps, or the self-service funding page a refusal reply links you to.³

The price you are quoted is the price you pay

A recipient can reprice a sender at any time, so the rate you were shown is not guaranteed to still be the rate when your purchase lands. Every purchase therefore carries a price ceiling: the per-stamp figure the client quoted you. If the price has moved above it in the meantime, the program refuses the purchase instead of charging you the new rate, and you can re-quote and decide again.

The ceiling is read fresh at the moment you buy, not when the quote was displayed — so it holds even if you left the page open, and it applies whether or not you asked for a quote first. It covers only the per-stamp postage; the protocol fee, the settlement surcharge and the one-off account rent are set by the protocol rather than the recipient, and cannot move under you the same way.

Getting unspent postage back

Prepaid postage is a deposit, not a payment: until a stamp is actually spent on a delivery, the lamports behind it are still sitting in the frombox. Two people can take them back out, and which one you are decides how.

The recipient can close the frombox outright, which reclaims the whole balance — the rent they put up plus whatever stamp value is left. That is their remedy against a sender who stockpiled cheap stamps before a price rise.

The sender can withdraw their own unspent postage without disturbing the account, provided the frombox is keyed on their wallet address rather than an email address. The stamp count drops to zero, the lamports return to the sender’s wallet, and the frombox stays open at the price the recipient set. A frombox keyed on an email string hashes text no wallet key can reproduce, so it has no sender-side withdrawal and stays the recipient’s to close.⁴

Withdraw from the webmail Balances pane: quote the recipient you prepaid, and a Reclaim unspent button appears beside the buy buttons once the frombox is shown to hold stamps. The button is offered only when you are sending as your own wallet address, because that is the only frombox the withdrawal can address — send as an alias or an email address and it is simply not there, rather than there and failing.

Because the recipient’s close still sweeps any residual left behind, the sender’s withdrawal is a way to move first, not an exclusive claim — see frombox custody for the reasoning behind that ordering.

1. From the terminal: Looking up a frombox. The CLI additionally annotates prices with a best-effort USD value (fail-soft — a rate-API outage just drops the annotation), mirroring sithbit earnings. ↩

2. From the terminal: Update a frombox. ↩

3. From the terminal: Add stamps. ↩

4. From the terminal: Reclaiming unspent stamps. ↩