**Cargo Mailboxes** is a feature of 📝Cargo that gives a workspace its own sending domains and inboxes, so plays, tools, and agents can deliver cold email through the native sendEmail action with pacing, suppression, and credit tracking handled by the platform. It exists because cold outreach from freshly registered domains needed a separate sequencer and rented inboxes, with replies and unsubscribes landing outside the system that decided to send. Built for 📝Go-To-Market (GTM) teams running outbound from Cargo, it is positioned for new-domain cold outreach rather than as a replacement for connected Gmail or Outlook accounts or transactional providers.
Evaluated for our outbound loop and not adopted as the send rail. A Google mailbox is 125 credits a month with a 40-send daily cap and 0.1 credits a send, so four mailboxes cost about the same as our existing 📝Smartlead plan at roughly 250 sends a day and more above it. Owned mailboxes make sense for a team without a sequencer; beside one that is already paid and warmed, they double the rail cost. Cargo stays our sourcing, enrichment, and verification system.
Key Capabilities
- Owned domains and inboxes —
defineDomainadopts or registers a sending domain anddefineMailboxmints a Google, shared, or private SMTP inbox on it; domain, username, and type are create-only. - Warm-up ramp and pacing — the daily ceiling climbs from 5 to 40 sends over 45 days after warm-up starts, and a spread policy paces one send every 24 hours divided by the ceiling.
- Native sending —
sendEmailtakes a mailbox, recipient, subject, and HTML body, threads replies throughinReplyToandreferences, and bills 0.1 credits per delivered email. - Workspace-wide suppression — unsubscribes, bounces, and manual entries opt a recipient out of the whole sender, and a suppressed address is refused before any message row is written.
- Thread events and triggers — sent, opened, clicked, replied, and unsubscribed land on the thread, and
waitEmailEventor an email trigger wakes a workflow or agent on reply.
Getting Started
- Buy or adopt a sending domain, then declare it with
defineDomain(domain, {adopt: true}). - Quote the monthly mailbox charge with
cargo-ai mailboxManagement pricing getbefore deploying. - Declare the inbox with
defineMailboxusing a real person's name and local part; deploy. - Start warm-up:
cargo-ai mailboxManagement mailbox start-warmup <uuid>on the same day. - Send a test to yourself via
sendEmailand confirm threading, tracking, and the unsubscribe link.