create-mail-attachment-upload-session

Create an upload session that allows an app to iteratively upload ranges of a file, so as to attach the file to the specified Outlook item. The item can be a message or event. Use this approach to attach a file if the file size is between 3 MB and 150 MB. To attach a file that's smaller than 3 MB, do a POST operation on the attachments navigation property of the Outlook item; see how to do this for a message or for an event. As part of the response, this action returns an upload URL that you can use in subsequent sequential PUT queries. Request headers for each PUT operation let you specify the exact range of bytes to be uploaded. This allows transfer to be resumed, in case the network connection is dropped during upload. The following are the steps to attach a file to an Outlook item using an upload session: See attach large files to Outlook messages or events for an example. 💡 TIP: For attachments 3MB to 150MB. Graph rejects smaller files with ErrorAttachmentSizeShouldNotBeLessThanMinimumSize, so under 3MB use add-mail-attachment instead. Body: { AttachmentItem: { attachmentType: 'file', name: 'report.pdf', size: 5000000 } }. Returns a pre-authenticated uploadUrl; the caller PUTs the bytes there itself in ranges up to 4MB. This server does not perform the PUT. It is categorised as a Write tool in the Ms 365 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

create-mail-attachment-upload-session accepts 5 parameters: body, confirm, messageId, includeHeaders, excludeResponse. Required: body, messageId. The full parameter table on this page comes from the server's own tool schema.

Register the Ms 365 MCP server in PolicyLayer and add a rule for create-mail-attachment-upload-session: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Ms 365. Nothing to install.

create-mail-attachment-upload-session is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Yes. Add a rate_limit block to the create-mail-attachment-upload-session rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

Set action: deny in the PolicyLayer policy for create-mail-attachment-upload-session. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

create-mail-attachment-upload-session is provided by the Ms 365 MCP server (@jo3zik/ms-365-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.