Send cold email with Sendsets

Sendsets is a cold email API for agents. Work through the Sendsets MCP tools when they are connected (list_mailboxes, create_campaign_draft, add_campaign_step, add_contact, start_campaign, list_threads, send_reply, ...). Otherwise use the sendsets CLI with --json. Both act on the same workspace.

Not connected yet? Pick one:

• MCP: claude mcp add --transport http sendsets https://api.sendsetsapi.com/v1/mcp (OAuth sign-in in the browser; other clients use the same URL)
• CLI: install with brew install addisonhoff/tap/sendsets (macOS, Linux) or scoop bucket add sendsets https://github.com/AddisonHoff/homebrew-tap then scoop install sendsets (Windows). Without a package manager, download the archive for your platform and checksums.txt from https://github.com/AddisonHoff/sendsets-releases/releases/latest, check the archive against checksums.txt, and unpack the sendsets binary onto PATH. Then sendsets login --hostname sendsetsapi.com (it prints a code and URL for the user to approve) and sendsets doctor --json

A new workspace is free for up to 10 mailboxes: https://app.sendsetsapi.com/auth/register

1. Senders

sendsets mailbox list --json. With no mailbox, connect one:

• Gmail or Google Workspace: the user creates an app password at https://myaccount.google.com/apppasswords and enters it themselves at https://app.sendsetsapi.com/app/emails (Connect mailbox, then Gmail). Never ask for a mailbox password in chat and never put one on a command line, where it lands in shell history and the process list
• Microsoft 365: sendsets mailbox add --provider outlook prints a consent link for the user
• Anything else over SMTP/IMAP: the user connects it in the same dialog with their host, port and password

Never guess credentials. A fresh mailbox should warm up first (sendsets mailbox warmup enable MAILBOX_ID) and start around 10 to 20 cold emails a day.

2. The campaign