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LinkedIn provides several APIs for messaging-related scenarios, but access is limited to specific products and use cases. Direct, general-purpose access to a personal LinkedIn inbox from a custom project is not described in the provided documentation.
From the available context, these are the supported, documented options:
- Communications (Invitations and Messages) APIs
LinkedIn exposes:- Invitation API – to send invitations to connect.
- Messages API – to send messages to existing connections.
These are described as allowing applications to use LinkedIn’s Inbox to send invitations and messages, effectively making an application a “social communications hub.”
Details and requirements (permissions, partner programs, rate limits, etc.) are not in the provided text, but the high-level capability is: send messages to existing connections and send invitations via API.
- Marketing Message Ads / Sponsored Messages
For advertising scenarios (not normal inbox DMs), LinkedIn supports:- Message Ads API – to set up and manage Message Ads that are delivered as sponsored messages into members’ InMail inboxes under an ad account.
- Message Ads are branded, paid messages with a call-to-action, optionally with Lead Gen forms, and are part of LinkedIn Marketing APIs.
- Message Ads are being discontinued starting May 2023, and the documentation recommends using Conversation Ads instead.
This is for paid campaigns, not arbitrary inbox access.
- Recruiter / Talent-specific InMail APIs
For LinkedIn Recruiter and CRM integrations (not general LinkedIn accounts), there are:- InMail History APIs (Recruiter System Connect and CRM Connect) – to retrieve InMail activity (sent and received) for a given LinkedIn Recruiter contract. These are intended for ATS/CRM integrations and require:
- A LinkedIn Recruiter contract.
- Seat URNs for Recruiter seatholders.
- Member URNs for prospects.
- Authorized access via the documented authentication flows.
- These APIs are designed to periodically pull InMail history (e.g., every 30 minutes, with a maximum 12‑hour time range per call) and support pagination.
- There is also a stub profile mechanism to create/update candidate records in an ATS based on InMail responses. These APIs are not generic inbox access; they are scoped to Recruiter contracts and candidate communication.
- InMail History APIs (Recruiter System Connect and CRM Connect) – to retrieve InMail activity (sent and received) for a given LinkedIn Recruiter contract. These are intended for ATS/CRM integrations and require:
- Dynamics 365 Sales + LinkedIn InMail
Dynamics 365 Sales integrates with LinkedIn to:- Use a Send InMail activity from within Dynamics to message customers who are not already connections.
- This is a productized integration; the InMail pane opens inside Dynamics and sends the message via LinkedIn.
This is not a generic API for arbitrary projects; it’s a built-in feature of Dynamics 365 Sales.
Summary for a custom ASP.NET/API project:
- The context confirms that LinkedIn has APIs to send messages (Messages API, Invitation API) and to send sponsored Message Ads and retrieve InMail history for Recruiter/CRM scenarios.
- Generic, full access to a user’s LinkedIn inbox (fetch all direct messages, send arbitrary DMs to any user) from a custom project is not described here.
- To send or retrieve messages programmatically, the project must fit into one of the supported scenarios:
- Use Communications APIs (Invitations/Messages) for messaging with existing connections, subject to LinkedIn’s access and permissions.
- Use Marketing Message Ads / Conversation Ads for sponsored messaging campaigns under an ad account.
- Use Recruiter InMail History APIs only if integrating with LinkedIn Recruiter/CRM and holding the appropriate contract and authorization.
For implementation, review the specific API documentation linked under:
- Invitation API
- Messages API
- Message Ads API
- Retrieve InMail History / InMail Stub Profiles and ensure the project meets the prerequisites (ad account, Recruiter contract, sender permissions, authentication, etc.).
References: