Use cases
One person at a time, on purpose.
Mailroom fits the moment a workflow owes a specific human a specific message. It is deliberately bad at everything else, and the second half of this page is the honest list of what that rules out.
Where it fits
Six jobs it does well.
The agent finished and someone needs to know
A long job ends at 3am. The person who asked for it is not watching a terminal. One message, to them, with the result and a link — the most common reason an autonomous workflow needs an outbound channel at all.
A handoff that needs a real reply
Ounie's Handoff app can put a decision page in front of a human. Sometimes what you want instead is an actual email thread they can reply to, forward, and keep. Set reply_to to the address that reaches you and you have one.
Answering one inbound person
A support agent drafts a reply to one customer. It has to come from a domain that delivers, carry an unsubscribe, and be attributable to the key that sent it if it goes wrong. That is exactly the shape of a single Mailroom call.
Transactional mail from a workflow
A receipt, a confirmation, a password-less link, a nightly digest for one recipient. Priced per message so a workflow that sends twelve emails a month costs less than a coffee, with no plan to right-size.
A keyless agent with a wallet
No Ounie account, no signup, no key rotation. POST, take the 402, sign, retry. Useful for one-off automations and for agents that hold USDC but have no relationship with anybody.
Testing an integration honestly
Send to the provider's mailbox simulator and get a real message id back without touching a human inbox. It is a real send, so it is billed like one — which is the point: your test exercises the same path as production.
Where it does not
Four jobs to take somewhere else.
Telling you this before you build is cheaper for both of us than letting you find out at the fourth ceiling.
A newsletter, an announcement, a launch
Any message you want many people to receive is the wrong shape for this API and would trip the recipient ceiling almost immediately. Ounie's Sequences product is the campaign tool, and it requires an account and a human.
Cold outreach at volume
Not because it is impossible to express as a loop, but because the ceilings and the automatic complaint revocation are built specifically to stop that loop. A key that gets complaints is cut off, and the ceilings will find you first.
Anything that needs an inbox
Mailroom does not receive. There is no address to provision and no message to poll. If your workflow is built around reading replies programmatically, this is not the tool — set reply_to to a mailbox you already own and read it there.
Sending from your own domain
The From address is always a verified Ounie sending domain. A caller-supplied From is how one tenant spends another's reputation, and an unverified one does not deliver anyway.
2 credits, one message.
If the job on your desk is one person at a time, this is the whole integration: mint a key, POST a message, read the id.