What you’re seeing
- Every employee's email to customers and vendors bounces back at roughly the same moment.
- The non-delivery report quotes 550 5.7.233 and says the organization has exceeded its external recipient rate limit.
- Internal email between coworkers still works normally while anything addressed outside the company fails.
- The problem began shortly after a newsletter, bulk invoice run or automated workflow sent a large batch of messages.
Common causes
Every environment is different, but these are the causes our engineers find most often:
- Exchange Online enforces a tenant-wide cap on external recipients per 24 hours, scaled to the number of licenses the organization holds.
- A marketing newsletter or mass announcement was sent from Microsoft 365 instead of a dedicated bulk email service.
- A Power Automate flow, CRM integration or billing app loops or sends far more messages than intended.
- A compromised mailbox is being used to blast spam or phishing to outside addresses, consuming the whole tenant's allowance.
- Small tenants with only a few licenses have a much lower ceiling, so even a modest campaign can hit it.
Why it matters
When the tenant limit trips, nobody can quote, invoice, reply to a customer or chase a payment by email until the rolling window clears. For a small company that can mean a full day of halted outbound communication. If the cause is a compromised account, the outbound spam can also damage your domain's reputation, so mail lands in spam long after the block lifts. Identifying what consumed the allowance matters as much as getting mail moving again.
How AskTechGurus fixes it
Skip the trial and error. A certified engineer works on your actual system, finds the root cause, and fixes it properly.
Tell us what’s happening
Submit a ticket in about two minutes. Paste the error, describe what changed, and pick your tier. No charge to submit.
A certified engineer diagnoses it
A vetted, US-based systems engineer claims your ticket, usually within minutes during business hours, and investigates over a secure remote session you can watch and end at any time.
Fixed and verified with you
The engineer resolves the root cause and confirms with you that it’s working. You don’t just get a workaround, and you get a plain-English summary of what was wrong.
Pay only when it’s resolved
Fixed price from $99, invoiced only after you approve the fix. If it isn’t resolved, you don’t pay.
Frequently asked questions
How long does the block last?
The limit works on a rolling 24-hour window, so mail starts flowing as older sends age out. Repeat triggers keep the organization blocked.
Could this be a hacked account?
Yes. A mailbox sending spam is a common cause, and if sent items show messages nobody recognizes, disconnect that user's devices from the network and treat it as a security incident.
Can AskTechGurus find what caused it?
A certified US engineer reviews mail traces and sending patterns with you over a remote secure session, from $99, and you pay only when it's resolved.