What the bounce says
Exact wording as it appears in the rejection or NDR. Placeholders such as x.x.x.x and example.com stand for your own address and domain.
550-5.4.5 Daily user sending limit exceeded. For more information on Gmail sending limits go to https://support.google.com/a/answer/166852 550 5.4.5 Daily SMTP relay limit exceeded for customer.
Google Workspace and Gmail cap how many recipients an account can address per day, and the SMTP relay service has its own per-domain cap. 5.4.5 means one of those rolling limits was reached; sending resumes as the window moves.
Most common causes
- The account sent more than its daily recipient limit
- A script or integration is sending through a user mailbox
- The SMTP relay service limit for the domain was reached
- A compromised account is sending bulk mail
What to verify next
- Identify which account or relay hit the limit from the rejection
- Check for compromise if the volume was unexpected
- Move bulk or automated mail to a proper sending platform
- Wait for the 24-hour window to reset; the limit is rolling
Which limit was hit
The text distinguishes a user limit from a relay limit. User limits apply to mail sent from a mailbox — including through a script using that mailbox’s credentials. Relay limits apply to the SMTP relay service configured for the domain.
Unexpected limit hits often mean an integration is sending through a user mailbox, or an account has been compromised and is sending bulk mail.
- User limit versus relay limit.
- Scripts on user mailboxes consume the user limit.
- Sudden limit hits can indicate compromise.
Move bulk mail off mailboxes
Notifications, campaigns and application mail belong on a sending platform or the Workspace relay with proper configuration, not on a person’s mailbox. That removes the limit problem and improves authentication.
Check for compromise
If nobody intended to send at volume, review the account’s sent mail and sign-in history, reset the password and revoke app passwords and OAuth grants.
Best diagnostic path
Mail Failure Doctor
Classify the complete rejection and preserve provider-specific diagnostic context.
Open analysis → Live analysisEmail Infrastructure Digital Twin
Map the domain’s public mail infrastructure and provider relationships before remediation.
Open analysis →Known limits
- Limits depend on the Workspace edition and trial status.
- The 24-hour window is rolling, not calendar-based.
Common questions
When can the account send again?
As the rolling 24-hour window moves; there is no fixed reset time.
Can the limit be raised?
Not per account. Use the SMTP relay service or a sending platform for higher volume.
Does Gmail count recipients or messages?
Recipients. One message to 500 addresses uses 500 of the daily allowance.
Why the exact message matters
The same status family can be triggered by different conditions, and providers frequently add diagnostic text that narrows the issue. Use the complete rejection text rather than treating the numeric code as a complete diagnosis.
Provider reference
For the provider-defined meaning and current requirements, review Google Workspace sending limits.