M365 refuses since we ran a new script with 4.7.500 or throttle
Microsoft 365 throttles per user and per tenant. Per user: 30 messages per minute, 10,000 recipients per day. Per tenant via Exchange Online relay: 10,000 recipients/day default. A 4.4.62, 4.4.7 or 4.7.500 cap means throttle, not permanent block.
Try this first
- 1Read the NDR. 4.7.500-901 = sender exceeded message rate. 4.7.28 = throttling. 5.0.350 = relay denied.
- 2Spread sending over time. 30/minute means a loop with sleep of 2 seconds between messages works past the cap.
- 3Batch jobs above 10k/day: don't use an M365 mailbox. Use an ESP or Azure Communication Services Email.
- 4SMTP relay from on-prem apps: use a Receive Connector with IP allowlist and dedicated quota, not user AUTH.
- 5Monitor in Exchange admin → Mailflow → Message Trace. You see per-user volume there.
When to bring us in
Sending more than 5k recipients/day from one mailbox routinely means you're on the wrong tool. Migrate to an ESP, it's cheaper and you keep reputation.
See also
- Our emails land in spam for some recipientsAlmost always an SPF, DKIM, or DMARC setting that is wrong or missing, or a sender name that mimics a well-known brand.
- Someone reports receiving phishing emails "from us"Read: spoofing. Someone is abusing your sender name, not necessarily your actual mailbox.
- An email bounces (NDR): delivery failedThe NDR text usually states the exact reason. Reading it is step one.
None of the above fits?
Describe your situation below. We pass your input plus the steps you already saw to our AI and return tailored next-step advice. If it's too risky to DIY, we'll say so.
Or skip the DIY entirely
Our Managed IT clients do not look these things up. One point of contact, a fixed monthly price, resolved within working hours.