specification: API Commons Rate Limits
specificationVersion: '0.1'
schema: https://raw.githubusercontent.com/api-evangelist/interface-research/main/schema/api-commons.yml#/$defs/RateLimits
provider: Microsoft Exchange
providerId: microsoft-exchange
created: '2026-05-04'
# Provenance stamped 2026-08-11: this artifact was written by the API Evangelist
# bulk sweep dated 2026-05-04, not harvested from the provider. See roadmap#35.
method: generated
modified: '2026-05-05'
reconciled: true
tags:
  - Rate Limiting
  - Email
  - Calendar
  - Exchange Online
  - Microsoft Graph
  - Microsoft
description: Microsoft Exchange Online enforces throttling at multiple layers — Microsoft Graph mail/calendar
  endpoints, Exchange Web Services (EWS), Exchange Online PowerShell, and the SMTP submission service
  — each with distinct policies. Limits are scoped per app/tenant or per mailbox/user. Returns 429 Too
  Many Requests with Retry-After.
sources:
  - https://learn.microsoft.com/en-us/graph/throttling-limits
  - https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/exchange-web-services/ews-throttling-in-exchange-online
  - https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/exchange-web-services/limits-for-active-connections-in-exo
headers:
  retryAfter: Retry-After
  requestId: request-id
  throttleScope: x-ms-throttle-scope
  throttleLimit: x-ms-throttle-limit-percentage
responseCodes:
  throttled: 429
  serviceUnavailable: 503
limits:
  - name: Exchange Message Trace Service
    scope: tenant
    metric: requests_per_5_minutes
    limit: 100
    timeFrame: minute
  - name: EWS — concurrent connections per app/mailbox
    scope: app/mailbox
    metric: concurrent_connections
    limit: 27
    notes: 27 concurrent connections per (application, mailbox) tuple in Exchange Online
  - name: EWS — total connections per mailbox
    scope: mailbox
    metric: concurrent_connections
    limit: 27
  - name: EXO PowerShell — concurrent runspaces
    scope: user
    metric: concurrent_runspaces
    limit: 3
    notes: 3 concurrent connections per user-account in Exchange Online PowerShell
  - name: SMTP submission per mailbox
    scope: mailbox
    metric: messages_per_minute
    limit: 30
    timeFrame: minute
    notes: 30 messages per minute per mailbox; 10,000 recipients per day per mailbox
  - name: Daily recipient cap per mailbox
    scope: mailbox
    metric: recipients_per_day
    limit: 10000
    timeFrame: day
  - name: Microsoft Graph global ceiling
    scope: application
    metric: requests_per_10_seconds
    limit: 130000
    timeFrame: second
policies:
  - name: Backoff Strategy
    description: Honour the Retry-After header on 429 from Graph and EWS; for HTTP 503 ServerBusy use
      exponential backoff with jitter.
  - name: Use Microsoft Graph for new development
    description: EWS is on a deprecation path; new mail / calendar code should target the Microsoft Graph
      mail and calendar endpoints.
  - name: Use change notifications
    description: Subscribe to Graph change notifications instead of polling for new mail.
  - name: Batch and delta queries
    description: Use $batch and delta queries to minimise request count.
  - name: SMTP relay for high volume
    description: For application-generated mail above mailbox SMTP limits, use a connector or third-party
      relay; 30 msg/min and 10K recipients/day are hard mailbox caps.
maintainers:
  - FN: Kin Lane
    email: kin@apievangelist.com