Social25 wont just sent any message to einstein. It depends on the conversation state and message types. This article explains how Social25 and Einstein interact.
Initial message
When you have Einstein connected to a Social25 channel, all conversations will be in the auto bot state. When a conversation is in the auto bot state, all inbound messages will be forwarded to einstein. Einstein can only handle inbound text messages. Other message types will be ignored by einstein.
Einstein will create a session id for the specific conversation. After 3 days this session is deleted and a new session will be created. At this point any context is lost.
Transfer to agent
If Einstein returns an escalate message, a handover is performed. At this point the conversation state is updated to open in Social25. Additionally an event message is added to the conversation. Depending on your configuration this message will trigger the creation of a case in Salesforce. At this point a service agent can continue the conversation in with the customer.
End chat
Einstein also can send an end session message. When this message is send. We clear up the session that is connected to the conversation. All context is lost and the conversation state won't be changed. When a new message is received a new session is created.
Errors
Einstein can handle errors within the Einstein flow itself using the Error Handler dialog. If something goes wrong calling Einstein or if Einstein is not activated, a hard coded message is send to the conversation telling the customer will be handover to an agent. At this point a handover is performed as described in the Handover section.