5.1.90: Daily recipient limit reached
Exchange Online returns 5.1.90 when your account has reached its daily limit for message recipients under Microsoft 365’s sending limits. Sending resumes as the rolling window clears. Microsoft also notes it can mean the account was compromised and is sending spam, so rule that out first.
The exact message
Microsoft 365 / Exchange Online
5.1.90 Your message can't be sent because you've reached your daily limit for message recipients
Why it happens
- More recipients in the last 24 hours than the account’s recipient rate limit allows.
- A compromised account sending spam.
How to fix it
- Check Sent Items for mail you did not send; if found, secure the account.
- Wait for the rolling 24-hour window to clear.
- Spread volume across more mailboxes instead of pushing one mailbox to its limit.
If you send cold email
Microsoft’s published limits are ceilings, not targets. Cold email mailboxes that run near them draw spam filtering long before they hit this bounce.
How WarmHawk handles it
WarmHawk never sends more than a mailbox’s own daily cap, spaces sends from one mailbox at least 8 minutes apart with random jitter, and starts a newly warmed mailbox at 5 campaign emails a day, growing 20% a day. A temporary failure is retried with backoff (30 minutes, then doubling) and the lead is suppressed after 4 attempts, so a throttled mailbox is never hammered. How WarmHawk works →
Related bounce codes
- 5.2.2Mailbox full, or submission quota exceeded
- 5.7.233Tenant exceeded its daily external recipient limit
- 5.1.8Access denied, bad outbound sender
Sources, checked 2026-09-29: Microsoft Learn: NDRs and SMTP errors in Exchange Online · Microsoft Learn: Exchange Online sending limits. Have a different bounce? Paste it into the decoder →
Questions
5.1.90 questions
What does 5.1.90 mean?+
Exchange Online returns 5.1.90 when your account has reached its daily limit for message recipients under Microsoft 365’s sending limits. Sending resumes as the rolling window clears. Microsoft also notes it can mean the account was compromised and is sending spam, so rule that out first.
Is 5.1.90 a temporary or permanent error?+
Permanent. The message will not be retried, and sending it again unchanged will fail the same way until the cause is fixed.
How do I fix 5.1.90?+
Check Sent Items for mail you did not send; if found, secure the account. Wait for the rolling 24-hour window to clear. Spread volume across more mailboxes instead of pushing one mailbox to its limit.