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create-mail-attachment-upload-session

Destructive

Create an upload session to attach large files (3-150 MB) to Outlook messages or events. Returns an upload URL for iterative PUT requests to resume interrupted transfers.

Instructions

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 large attachments (3-150MB). Body: { AttachmentItem: { attachmentType: 'file', name: 'report.pdf', size: 5000000 } }. Returns a pre-authenticated uploadUrl for direct PUT of file bytes.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bodyYes
messageIdYesPath parameter: messageId
includeHeadersNoInclude response headers (including ETag) in the response metadata
excludeResponseNoExclude the full response body and only return success or failure indication
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description discloses key behavioral aspects: iterative uploads, return of pre-authenticated upload URL, resumability via request headers, and the process after session creation. While annotations indicate destructiveHint=true and openWorldHint=true, the description adds value beyond annotations without contradiction. However, it does not detail authorization or rate limits, which could be useful.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is informative and logically structured, starting with the purpose, then usage guidance, steps, and a tip. While it is somewhat lengthy, each sentence serves a clear purpose, and the formatting (including the tip) aids readability.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the moderate complexity (file size constraints, upload session, PUT operations), the description covers the essential aspects: purpose, size limits, alternative, return value, and an example. It references external examples for further details. Without an output schema, the description still provides enough context for an AI to use the tool effectively.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Despite incomplete schema coverage for the 'body' parameter (empty properties, additionalProperties allowed), the description provides a concrete example of the AttachmentItem structure (attachmentType, name, size). It also explains the optional includeHeaders and excludeResponse parameters. The description compensates for the schema gaps.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool creates an upload session for attaching large files (3-150 MB) to an Outlook item, and explicitly distinguishes from the alternative POST method for smaller files. It also mentions the return of an upload URL, making the purpose highly specific and distinguishable from siblings like 'add-mail-attachment'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit when-to-use (file size between 3 and 150 MB) and when-not-to-use (under 3 MB, use POST) guidance. It includes steps, a tip with an example body, and references detailed examples, giving comprehensive usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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