Microsoft Outlook · Rate Limits

Microsoft Outlook Rate Limits

Outlook programmatic access is via Microsoft Graph mail / calendar / contacts endpoints (preferred), Exchange Web Services (legacy), and the deprecated Outlook REST v2.0. Throttling is enforced per app/mailbox and at the Microsoft Graph global ceiling. SMTP submission and recipient caps apply to Exchange Online mailboxes regardless of API used. Returns 429 with Retry-After.

Microsoft Outlook Rate Limits is the machine-readable rate-limit profile for Microsoft Outlook on the APIs.io network, in the API Commons Rate Limits shape.

It captures 7 rate-limit definitions, measuring requests_per_10_seconds, concurrent_connections, messages_per_minute, recipients_per_day, and varies.

Limit state is signalled in the retryAfter, requestId, throttleScope, and throttleLimit response headers, and an exhausted limit returns HTTP 429.

This profile was written by API Evangelist and has not been verified against a page the provider published; treat every limit as unconfirmed until a dated transcription replaces it.

The profile also includes 5 backoff/retry policies defined and response codes documented for throttled and serviceUnavailable.

Tagged areas include Rate Limiting, Email, Calendar, Outlook, and Microsoft Graph.

7 Limits Exhausted: HTTP 429 retryAfterrequestIdthrottleScopethrottleLimit
Method: generated, dated 2026-05-05.
Written by API Evangelist on 2026-05-05 and not verified against a page the provider published. Treat every limit as unconfirmed until a dated transcription replaces it.
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Rate LimitingEmailCalendarOutlookMicrosoft GraphMicrosoft

Limits

Microsoft Graph global ceiling application
requests_per_10_seconds · second
130000
EWS — concurrent connections per app/mailbox app/mailbox
concurrent_connections
27
Hard cap of 27 concurrent EWS connections per (application, mailbox) tuple
EWS — total per mailbox mailbox
concurrent_connections
27
SMTP submission per mailbox mailbox
messages_per_minute · minute
30
SMTP recipients per mailbox mailbox
recipients_per_day · day
10000
Outlook (mail / calendar / contacts) on Microsoft Graph app/mailbox
varies
per-mailbox throttling — fall back to Retry-After. No fixed numeric per-second value published.
Identity & Access (read) per app/tenant (used for user lookups) app/tenant
resource_units_per_10_seconds · second
3500–8000 RU per 10s based on tenant size

Policies

Backoff Strategy
Honour Retry-After on 429; the Microsoft Graph SDKs implement this automatically.
Use Microsoft Graph over EWS / Outlook REST
EWS is on a deprecation path and Outlook REST v2.0 is deprecated for work / school accounts; target Microsoft Graph for new development.
Use change notifications
Subscribe to mail and calendar change notifications instead of polling.
SMTP relay for high volume
For application-generated mail above mailbox SMTP caps, use a connector or a third-party relay; the 30 msg/min and 10K recipients/day limits are hard caps.
Use $batch
Combine related calls in $batch envelopes; each is throttled individually but network overhead is reduced.

Sources

Work with this as data

Every rate limit here is available over the APIs.io API and to AI agents over MCP.

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Tools for rate limits

4 MCP tools reach this
  • find_rate_limitsBrowse and filter every rate limit in the catalog.
  • apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
  • resolveTurn a domain, URL or GitHub org into the provider it belongs to.
  • find_cohortsEvery scored population of providers in the catalog.
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Call it yourself

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This rate limit 
curl "https://apis.io/api/v1/rate-limits/microsoft-outlook-rate-limits"
All rate limits 
curl "https://apis.io/api/v1/rate-limits?limit=25"

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