Enhanced Status Code 5.1.90: Daily Recipient Limit Reached
Enhanced Status Code 5.1.90 means “Daily Recipient Limit Reached.” The sending mailbox has reached its daily recipient limit in Microsoft 365. Numbered 5.x but functionally temporary, since the allowance resets, so the recipients must not be suppressed.
550 5.1.90 Your message can't be sent because you've reached your daily limit for message recipientsWhat does 5.1.90 mean?
Microsoft returns 5.1.90 when a sending mailbox has reached its daily limit for message recipients. Exchange Online caps each mailbox at a fixed number of recipients per day, counted per recipient rather than per message, and the cap applies to the account rather than to any particular message.
The numbering deserves comment. Microsoft assigns it a 5.x code, which conventionally means permanent, but the condition is a quota that resets. Treating it as a hard bounce and suppressing the recipients would remove perfectly valid addresses over a sender-side limit that clears within a day. That is why this reference classifies it as temporary despite the leading digit: the correct action is to wait and resend, never to suppress.
The underlying issue is nearly always that bulk or automated sending is running from a person's mailbox. Exchange Online mailboxes are provisioned for individual correspondence, and their limits reflect that. Any application sending at volume belongs on a connector, on a high volume mail service, or on a dedicated transactional provider, all of which have limits designed for the purpose.
How 5.1.90 plays out
5.1.90 replyWhere 5.1.90 sits: soft vs hard bounce
| Soft bounce (4xx) | Hard bounce (5xx) | |
|---|---|---|
| Nature | Temporary | Permanent |
| SMTP class | 4xx | 5xx |
| What to do | Let it retry | Suppress the address |
| Recoverable? | Often | No |
| 5.1.90 is | ✓ this code |
What each provider means by 5.1.90
A registered code does not oblige a provider to use it that way, and the large ones diverge. Match the wording in your own bounce, not the definition above.
Common causes of 5.1.90
- The mailbox exceeded its daily recipient allowance in Exchange Online
- A message with a large recipient list consumed the allowance in one send
- An application is sending bulk mail from an individual user mailbox
- Several applications share one mailbox and their volumes accumulate
- A retry loop resent the same messages and consumed the quota
- A distribution list expanded to more recipients than expected
How to fix 5.1.90
- Do not suppress the recipients, since the limit belongs to your account rather than to them
- Wait for the allowance to reset and resend
- Move bulk and automated sending off individual mailboxes onto a connector or relay
- Count recipients rather than messages when estimating usage
- Give each application its own sending identity so one cannot exhaust another
- Check for retry loops, which can consume a daily allowance in minutes