Smartlead (Gold)

The deepest connection of the senders. You paste an API key, register webhooks, and sends, opens, clicks, replies, bounces and lead category changes start landing on the contact. Thread history is stripped so a HubSpot email activity shows the newest reply instead of the whole quoted chain.

Instantly (Gold)

Same API key and webhook pattern, covering campaign sends, engagement events and replies. The docs carry a dedicated page on diagnosing missing Instantly replies, which tells you where this one tends to wobble, usually around webhook registration and lead status changes.

HeyReach (Gold)

The LinkedIn side. Connection requests, acceptances, messages and replies sync as activity, and because social profiles are not email addresses there are separate lookup options and a guide for handling profile URLs so the record matches the right person.

EmailBison (Gold)

Full parity with the email tools including automated reply detection, which matters because EmailBison sits with agencies running many client workspaces. This is one of the few CRM sync routes EmailBison has, so the pairing carries more weight than it looks.

HubSpot (Gold)

A marketplace app installed by OAuth. It writes email engagements, app timeline events, more than fifty contact properties and contact and company associations, reads HubSpot lists to build block lists, and works on every HubSpot tier, although workflows and attribution reports need Professional. OutboundSync counts 1,500 plus app installs across its platforms.

Salesforce (Gold)

Connected through an External Client App rather than a managed package. Activity writes to Tasks against Leads and Contacts across more than fifty fields, Flows can trigger on it, block lists come off a Salesforce report, and API call consumption is the real constraint, so Enterprise or Unlimited is the sane home.

Clay (Silver)

Listed as a source, so Clay can push enriched contacts and activity in the same way a sender does. OutboundSync argues against using Clay as the sync layer itself on table row limits and payload truncation, and their framing of the two as complementary is fair enough.

Pipedrive, Close, Attio and HighLevel (beta)

All four are beta CRM connections that write one-way plain-text Notes on the person record, with no block list return path and no prebuilt views. Pipedrive is in the Pipedrive Marketplace for OAuth, but onboarding on all four still runs with the OutboundSync team, so treat them as a preview and confirm the current state on a call before you plan reporting around them.

The long tail (Bronze)

The rest of the 21 sales engagement platforms, including Lemlist, Reply.io, Mixmax, Brevo, Salesforge, SalesRobot, Aimfox, Drippi, GetSales, PlusVibe, SuperSend, Expandi and Salesflow, plus Salesfinity for dialing and inbox managers like Masterinbox and HotHawk. Coverage here is real but thinner in the docs than the Gold six.

API, MCP, webhooks and agent skills

Every plan ships four agent surfaces, all in beta. The REST API at app.outboundsync.com/api/v1 has an OpenAPI 3.1 contract and read endpoints for connections, sources, prior outreach per contact and sync attempts, plus write scopes for retries and blocklist pauses. The hosted MCP at mcp.outboundsync.com wraps about 35 of those routes for Cursor, Claude Code and Codex over a Bearer key. Webhooks deliver sync.failed and sync.recovered to your own HTTPS endpoint with signed payloads and retries. Fifteen public skills install with npx skills add outboundsync/skills and cover launch preflight, sync monitoring, CRM analysis and cold email copy.

What is missing

No Outreach, Salesloft or Apollo on the sending side, and no Zoho or Copper on the CRM side, so this is squarely a cold-outbound-into-HubSpot-or-Salesforce product with four beta CRMs around it. Zapier, Make and n8n are treated as competitors rather than partners, so there is no glue-tool path into a CRM they do not support. Claude Desktop connectors are not supported yet because the MCP expects a Bearer key rather than OAuth.