What happens when you exceed the limit
Throttling (message rate) or NDR 550 5.7.233/234-class tenant limit errors once TERRL is hit. That is the documented behavior. The undocumented one matters more: a mailbox that repeatedly runs into its cap is behaving the way Microsoft 365's filters expect a bulk sender to behave, and the reputation cost outlasts the block. Treat the published figure as a ceiling to stay well under, not a daily target.
How the limit interacts with a warmup ramp
New tenants and onmicrosoft.com senders are heavily restricted; add a custom domain and warm before outreach. A warmup ramp and a provider cap are two different ceilings. The cap is where Microsoft 365 stops you; the ramp is where reputation would stop you first. MailStrike's default ramp climbs to 30 warming emails a day per mailbox over 21 days, and real outreach starts at 20 to 30 a day once the ramp is done. Against Microsoft 365's 10,000 recipients per mailbox per day, the ramp never comes close; the cap is not the constraint, reputation is. Set the provider, the domain's age and the target volume below to see the schedule.
| Outreach a day, per mailbox | 1 mailbox | 2 mailboxes | 3 or more |
|---|---|---|---|
| Not sending yet | 30 | 21 | 18 |
| 10 emails | 30 | 21 | 18 |
| 20 emails | 25 | 18 | 15 |
| 30 emails | 20 | 14 | 12 |
| 40 emails | 15 | 11 | 9 |
| 50 emails | 10 | 7 | 6 |
The rule behind the table: a mailbox on its own that is not sending yet warms at the plan default of 30 a day, and once outreach starts it drops one warming email for every two you send, down to a floor of 10. Put a second mailbox on the domain and each one needs 70% of that figure, three or more and each needs 60%, because the domain earns the signal across all of them. Volume is a setting per mailbox, so you can dial these in directly.
The full setup for this provider, from the connect to the day the dashboard says the mailbox is safe to send from, is on the Microsoft 365 warmup page.
Trial, free tier and new-account restrictions
trial tenants capped at 5,000 external recipients/24h. New accounts and trials sit under tighter limits because they have no history, which is the same reason receivers distrust them. A ramp that respects the lower limit is also the ramp that builds the history.
The bounces these limits produce
Going over a limit shows up as a bounce, not a warning. The rate-limit codes from Microsoft in the bounce code decoder, each with its message and the fix:
- 550 5.7.233: tenant external recipient limit
- 550 5.7.236: onmicrosoft.com daily limit
- 550 5.2.2: submission quota exceeded
The bulk sender rules are a separate limit
None of the caps above is the line that decides placement. Google's and Yahoo's bulk-sender requirements and Microsoft's 2025 high-volume rules set authentication, spam-rate and unsubscribe conditions that apply well below any sending cap; the sender requirements page has them provider by provider, and the auth checker tests a domain against them.
How Microsoft 365 compares
documented cap per day (log scale); basis differs per provider
- Outlook.com sending limits
- Zoho Mail sending limits
- Yahoo Mail sending limits
- iCloud Mail sending limits
- Amazon SES sending limits
- SendGrid sending limits
Questions about Microsoft 365 sending limits
What is the Microsoft 365 sending limit per day?
Recipient rate limit 10,000 recipients per mailbox per 24h. Recipients per day: 10,000 per mailbox; tenant-wide External Recipient Rate Limit (TERRL) = 500 × licenses^0.7 + 9,500 per 24h for paid tenants; trial tenants 5,000/24h; onmicrosoft.com domains 100 external/24h. Source: Microsoft 365's own documentation, checked 6 Sep 2026 (page dated 2026-04-07).
What happens when you exceed the Microsoft 365 sending limit?
Throttling (message rate) or NDR 550 5.7.233/234-class tenant limit errors once TERRL is hit. Hitting the limit is also a reputation event: a mailbox that keeps running into it looks like a bulk sender to the provider's filters, so treat the limit as a ceiling you never approach rather than a target.
How many recipients per message does Microsoft 365 allow?
Up to 1,000 (admin-configurable); 5,000 for meeting invites.
How do I increase the Microsoft 365 sending limit?
trial tenants capped at 5,000 external recipients/24h. Beyond the published caps there is no setting to raise them; the limit you hit first in practice is reputation, not the cap. A warmed mailbox that never approaches the hard limit sends more reliably than a fresh one that tests it.
Is there a Microsoft 365 rate limit per minute or per hour?
30 messages per minute (throttled, not blocked).
Does the Microsoft 365 limit change how you warm up?
New tenants and onmicrosoft.com senders are heavily restricted; add a custom domain and warm before outreach.