Inbox & Reply Agents

Inbox

intent is one of: UNCLASSIFIED, INTERESTED, NOT_INTERESTED, OUT_OF_OFFICE, WRONG_PERSON, UNSUBSCRIBE_REQUEST, QUESTION.

OUT_OF_OFFICE is only for automatic replies: the message has Auto-Submitted, X-Autoreply or Precedence: auto_reply, a subject like “Automatic reply:” or “Out of Office”, or an unmistakable out-of-office phrase in its text. A reply a person wrote is not classified as OUT_OF_OFFICE.

Conversation list

Each row of GET /replies/threads has:

• latestReply: id, rawBody, intentClassification, receivedAt, remindAt, starred, and from ({ name, address } of who wrote it: the lead, or a colleague answering for them; null on replies received before 1 Oct 2026).
• unreadCount: their replies in this conversation nobody has opened yet.
• answered: true when you replied after their latest message. lastAnsweredAt is when.
• replyCount, lead, mailbox, campaign.

Conversation

GET /replies/thread/:leadId returns lead and messages, oldest first. Each message has direction (inbound or outbound), timestamp, subject, body, mailboxEmail, to and cc.

• Inbound messages also have from, html (the HTML as received, or null), attachments, intentClassification, remindAt and starred.
• Your own replies (kind: "reply") also have bcc, html, attachments, sentBy (HUMAN, API or AGENT), and status: SENDING, SENT or FAILED (with the reason in error).
• Campaign emails (kind: "campaign") also have campaign.

Addresses are { name, address }. Each attachment is { id, filename, contentType, size }; download it with GET /replies/attachments/:id.

Received files are kept up to 15 MB per file and 25 MB per message. Inline images (such as a signature logo) are skipped.

Answers written directly in Gmail or Outlook are picked up from the mailbox’s Sent folder (IMAP mailboxes) and show in the conversation as your replies, with sentBy: "HUMAN".

Sending a reply

POST /replies/:id/send body:

Set cid on an image shown inside html as src="cid:<cid>". It is then sent as an inline image.

For large files, upload them first with POST /replies/uploads while the reply is being written, then send their ids in uploadIds. The send then only sends the email. The upload body is the raw file with Content-Type: application/octet-stream; the file name goes in the X-Filename header (URL-encoded) and its type in X-Content-Type. An upload that is never sent is removed after a day.

curl -X POST https://api.sendboxes.tech/v1/replies/uploads \
  -H "Authorization: Bearer sb_live_..." \
  -H "Content-Type: application/octet-stream" \
  -H "X-Filename: Pitch%20Deck.pdf" -H "X-Content-Type: application/pdf" \
  --data-binary @"Pitch Deck.pdf"

curl -X POST https://api.sendboxes.tech/v1/replies/REPLY_ID/send \
  -H "Authorization: Bearer sb_live_..." -H "Content-Type: application/json" \
  -d '{
    "body": "Thanks Sam, Tuesday works.",
    "to": ["[email protected]"],
    "cc": ["[email protected]"]
  }'

Returns { sent, sentReplyId, sentAt } once the mail server has accepted the reply. Attachments over 20 MB in all return 413.

With "background": true the request does not wait for the mail server, which can take up to a minute to accept a large attachment. It returns 202 with { queued, status: "SENDING", sentReplyId }. The reply shows in the conversation right away with status: "SENDING", then SENT, or FAILED with the reason in error. A failed reply is never sent again on its own: send it again with POST /replies/sent/:id/retry. A reply still SENDING after 10 minutes shows as FAILED and can be retried. The dashboard always sends this way.

AI settings

Reply agents

tone is one of: PROFESSIONAL, FRIENDLY, CASUAL, FORMAL.