550 5.1.90: Microsoft daily recipient limit reached
550 5.1.90Daily recipient limit reachedPermanent: retrying will not helpFrom Microsoft 365 and Outlook.com
550 5.1.90 Your message can't be sent because you've reached your daily limit for message recipients
What it means
This bounce is generated by Microsoft for mail you sent. Your mailbox crossed a 24 hour cap on how many recipients it may address, so further sends are refused for a while. It typically reads like the example above. It is mostly seen on Outlook.com and on Microsoft 365 accounts with tight sending limits.
Unlike 5.1.8, which is a block after spam detection, 5.1.90 is a quota. The account is not considered compromised; it has simply addressed too many people in the rolling window. Each recipient on To, Cc, and Bcc counts, and a distribution list expanded by the sender’s client can count as many recipients.
Likely causes
- A newsletter or announcement sent to a long Bcc list from a personal mailbox.
- A mail merge or script that sends one copy per recipient through the mailbox.
- A new Outlook.com account, which starts with lower sending limits until it builds a history.
- A compromised account pushing spam, which can trip the limit before other protections act.
How to fix it
- Stop sending from the mailbox and wait for the rolling 24 hour window to clear; the limit lifts on its own.
- Check the Sent Items folder for messages you did not send. If you find any, change the password and enable two step verification.
- Split large announcements into smaller batches over several days, or send to a distribution group that the server expands instead of a long recipient list.
- Move newsletters and marketing mail to a bulk email service built for that volume.
Checks that apply
- Microsoft Compliance Checks your domain against Microsoft’s sender requirements, which matters once you move bulk mail to a proper sending service.
- SPF Check When you add a bulk sender, confirms its include is in your SPF record without breaking the 10 lookup limit.
FAQ
- How long until I can send again?
- Typically up to 24 hours, because the window is rolling. Sending more attempts in the meantime does not help.
- Can support raise the limit?
- Microsoft 365 admins can adjust some recipient limits per mailbox, but the tenant wide outbound limits are fixed. Outlook.com limits are not adjustable by you.