The honest answer is "it depends which path you take," because DimeBox prices the pieces of sending an email separately rather than bundling them into one "send an email" price. Here's the arithmetic for every path that ends with a message actually leaving an inbox, using the prices documented in the API reference.
POST /api/inboxes/{slug}/send accepts a drafted request shape - to, purpose, optionally tone and key_points - on any inbox that has AI drafting enabled (the default). One call, one price:
curl -X POST https://dimebox.app/api/inboxes/acme-support/send \
-H 'Content-Type: application/json' \
-H 'PAYMENT-SIGNATURE: <signed payment>' \
-d '{"to":"[email protected]","purpose":"follow up after demo call"}'
# $0.01, one callThat's the cheapest way to get a drafted email out the door: $0.01 total. See drafted vs raw send modes and what the drafting parameters actually do for how to shape that request.
If you want to see - or let a human review - the generated subject and body before it goes out, draft it standalone with POST /api/emails/generate first, then send the resulting text as a raw send:
curl -X POST https://dimebox.app/api/emails/generate \
-H 'Content-Type: application/json' \
-H 'PAYMENT-SIGNATURE: <signed payment>' \
-d '{"recipient":"[email protected]","purpose":"follow up after demo call"}'
# $0.02 - returns { "email": { "subject", "body" } }
curl -X POST https://dimebox.app/api/inboxes/acme-support/send \
-H 'Content-Type: application/json' \
-H 'PAYMENT-SIGNATURE: <signed payment>' \
-d '{"to":"[email protected]","subject":"...","body":"..."}'
# $0.01 - raw send of the text from the previous callTotal: $0.03 across two calls. You pay an extra cent over path 1 for the ability to inspect - or edit, or reject - the drafted text before it's sent. See the anatomy of a drafting call for what that $0.02 actually returns.
If the agent already has exact text to send - generated by its own model, or not drafted at all - it skips drafting entirely and pays only the send price:
curl -X POST https://dimebox.app/api/inboxes/acme-support/send \
-H 'Content-Type: application/json' \
-H 'PAYMENT-SIGNATURE: <signed payment>' \
-d '{"to":"[email protected]","subject":"Hi","body":"exact text here"}'
# $0.01, one callThis is also the only option on an inbox provisioned with ai_drafting_enabled: false - a purpose field sent to that inbox is rejected with a 422 rather than silently drafting. See disabling AI drafting.
None of the above covers provisioning the inbox itself. A free random-slug inbox costs $0 (throttled to three per IP per day); a custom name costs $1.00, once, no matter how many emails that inbox eventually sends. Neither number above includes receiving a reply, either - that's free over ordinary SMTP, or $0.03 per message if you need the priority, guaranteed-delivery channel instead. See the full cost picture of giving an agent an email identity, which covers provisioning and receiving alongside sending.
Because every path above resolves to a fixed number of calls at fixed prices, the cost of any volume of email is just multiplication, not estimation. An agent sending a run of drafted emails through path 1 costs the per-email price times the count, full stop - no tier boundary where the per-email price changes, no volume discount to negotiate, no overage rate that kicks in after some threshold. The same is true of path 2's $0.03 and path 3's $0.01. See budgeting for a fleet of agents for how to turn that per-email number into a daily or weekly ceiling once you know roughly how many emails a given agent is expected to send.
Reading is the one piece of this that never shows up on the bill at all. GET /api/inboxes/{slug}/messages and the single-message variant are both free, gated only by the X-Inbox-Token header - an agent can poll its own inbox as often as it wants to check for a reply without that polling adding anything to the numbers above. The cost model only prices the things that cost DimeBox something to do on your behalf: generating text, queuing a send, or guaranteeing a priority delivery. Looking at what's already there costs nothing, no matter how often you look.
If you only need one thing - get a drafted email out the door, trusting the drafting enough not to need a human or a second system reviewing it first - $0.01 is the actual floor. Everything above that is paying for either a review step (path 2's extra cent) or a different receive guarantee, not a hidden surcharge on the send itself.