Is there any limit on the payload size of a POST request in Graph API. This link suggests a limitation of 4MB. Is there any reference to this in the documentation?
Also is there any limitation for the outlook REST API
That is correct, individual requests to Microsoft Graph must be 4MB of less. An example from the documentation for /attachments:
Since there is currently a limit of 4MB on the total size of each REST request, this limits the size of the attachment you can add to under 4MB.
来源：https://stackoverflow.com/questions/46545077/microsoft-graph-api-is-there-any-limit-on-payload-size-of-a-post-request