Our app can't send more than X mails per hour via Office 365 SMTP
Microsoft 365 SMTP relay has hard limits: 10,000 recipients per day per user, 30 messages per minute.
Try this first
- 1Audit daily volume per application
- 2Under 10k/day/user: stay on O365 but split across multiple accounts
- 3Above that: switch to a dedicated relay (SendGrid, Brevo, AWS SES)
- 4For transactional, always use dedicated, not O365
When to bring us in
For ad-hoc spikes (e.g. newsletter batch): use a separate ESP, don't abuse O365 relay.
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?
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Or skip the DIY entirely
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