What 550 5.7.233 means
The message Microsoft attaches to this code is “Your message can't be sent because your tenant exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit)”, as written on its reference page. The first digit says how final it is: a 5xx reply is permanent for that message, so the sending server gives up and returns a bounce. The enhanced status 5.7.233 says what class of problem it is: rate limit. The sender exceeded a published cap or was throttled. Slow down and spread the volume; the cap resets.
Why it happens
The sender pushed more mail at the receiver, in a burst or across the day, than it is willing to take from a sender it does not know well. The limit is not only the published cap: a new domain sending its first hundred messages in one hour is throttled where an established one would not be.
What to do first: The tenant hit Exchange Online's external recipient rate limit (500 × licenses^0.7 + 9,500 a day). Wait for the window; spread sending across the day.
Why warming does not fix this
Warming builds sender reputation. 550 5.7.233 in this form is a rate limit problem, and no amount of engagement history changes it. Fix the cause and the bounce stops; warming is for what comes after, when the mail is accepted and the question becomes which folder it lands in. See how warming works for that part.
How to fix it, in order
- Slow the send and spread it across the day
- Check the provider's published limit
- Start outreach at 20 to 30 a day per mailbox and scale with placement, not with the cap
Related codes
- 550 5.7.236 (Microsoft): onmicrosoft.com daily limit
- 550 5.2.2 (Microsoft): submission quota exceeded
- 421 4.7.0 (Gmail): try again later
- 452 4.5.3 (Gmail): too many recipients
- 550 5.4.5 (Gmail): daily sending limit exceeded
More on Microsoft 365
- Microsoft 365 emails going to junk: the trace in order: headers, Message Trace, quarantine, SNDS
- Microsoft bulk sender requirements: the 5 May 2025 authentication rules and the 550 5.7.515 rejection
- Microsoft 365 sending limits: the documented recipient and message rate limits
Questions about 550 5.7.233
What does 550 5.7.233 mean?
Microsoft returns 550 5.7.233 with the message "Your message can't be sent because your tenant exceeded its daily limit for sending email to external recipients (tenant external recipient rate limit)": tenant external recipient limit. The sender exceeded a published cap or was throttled. Slow down and spread the volume; the cap resets.
Is 550 5.7.233 a hard bounce or a soft bounce?
A hard bounce for that message: the 550 reply is permanent, and the message is not retried. Whether the address should be removed depends on the cause: here the fix is on the sending side, not the list.
How do I fix 550 5.7.233?
The tenant hit Exchange Online's external recipient rate limit (500 × licenses^0.7 + 9,500 a day). Wait for the window; spread sending across the day. Microsoft's own reference for the code is linked on this page.
Does email warmup fix 550 5.7.233?
No. 550 5.7.233 in this form is a rate limit problem, and warming builds reputation, which is not what is failing here. Fix the cause and the bounce stops.