Microsoft Exchange · Rate Limits

Microsoft Exchange Rate Limits

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.

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

It captures 7 rate-limit definitions, measuring requests_per_5_minutes, concurrent_connections, concurrent_runspaces, messages_per_minute, and recipients_per_day.

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, Exchange Online, 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.
View Source
Rate LimitingEmailCalendarExchange OnlineMicrosoft GraphMicrosoft

Limits

Exchange Message Trace Service tenant
requests_per_5_minutes · minute
100
EWS — concurrent connections per app/mailbox app/mailbox
concurrent_connections
27
27 concurrent connections per (application, mailbox) tuple in Exchange Online
EWS — total connections per mailbox mailbox
concurrent_connections
27
EXO PowerShell — concurrent runspaces user
concurrent_runspaces
3
3 concurrent connections per user-account in Exchange Online PowerShell
SMTP submission per mailbox mailbox
messages_per_minute · minute
30
30 messages per minute per mailbox; 10,000 recipients per day per mailbox
Daily recipient cap per mailbox mailbox
recipients_per_day · day
10000
Microsoft Graph global ceiling application
requests_per_10_seconds · second
130000

Policies

Backoff Strategy
Honour the Retry-After header on 429 from Graph and EWS; for HTTP 503 ServerBusy use exponential backoff with jitter.
Use Microsoft Graph for new development
EWS is on a deprecation path; new mail / calendar code should target the Microsoft Graph mail and calendar endpoints.
Use change notifications
Subscribe to Graph change notifications instead of polling for new mail.
Batch and delta queries
Use $batch and delta queries to minimise request count.
SMTP relay for high volume
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.

Sources

Work with this as data

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

MCP server

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https://apis.io/mcp

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.
All 92 tools →

Call it yourself

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

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