Who This Is For / When to Use
Account owners sending emails through Kyrios
Users seeing failed, rejected, or delayed email messages
Anyone troubleshooting Mailgun or Google Workspace email delivery issues
How to View Email Error Details
When an email fails to send, Kyrios displays an error indicator in the email logs.
Steps to View the Error
Go to Settings > Email > Logs.
Locate the failed email.
Click the Actions (gear icon).
Select Quick view to see the delivery error message.
This view shows whether the failure is temporary or permanent and includes the exact error returned by the email provider.
Error #1: The Domain Is Not Allowed to Send
Error Message
“The domain is not allowed to send.”
Cause
The sending domain is not fully verified in Mailgun or required DNS records are missing or outdated.
How to Fix
Log in to your Mailgun account.
Open the Sending tab.
Click Domain Settings.
Select the correct domain from the dropdown at the top.
Open DNS Records.
Click Verify DNS Settings.
Confirm all required DNS records show a green checkmark.
If records already appear verified, click Verify DNS Settings again to force a refresh.
Error #2: The Domain Is Not Allowed to Send – Account Terminated
Error Message
“The domain is not allowed to send: Account Terminated.”
Cause
Mailgun has suspended or terminated the sending account.
How to Fix
Contact Kyrios support.
Kyrios will escalate the issue to the appropriate Mailgun team to determine the cause and next steps.
Error #3: Too Old
Error Message
“Too old.”
Cause
The email message expired before delivery could complete.
How to Fix
Contact Mailgun support directly.
This error requires provider-level investigation.
Error #4: Mailgun Send Verification Error
Common Error Examples
Sender verify failed
The domain of the sender address does not exist
Could not resolve sender domain
Your domain has no DNS/MX entries
Requested action not taken: mailbox unavailable
Cause
Sender address verification fails because Mailgun cannot validate the sending domain or mailbox.
How to Fix (Subdomain Sending – Recommended)
Set MX records for the sending domain to Mailgun:
mxa.mailgun.org(Priority 10)mxb.mailgun.org(Priority 10)
Wait 24–48 hours for DNS propagation.
Retry sending the email.
Additional Fixes
Ensure the From address domain exactly matches the Mailgun sending domain.
If using a root domain with an existing email provider, create a dedicated sending domain for Mailgun and configure MX records there.
Important Notes
Only point MX records to one provider to avoid email loss.
If needed, enable a catch-all mailbox with your email provider.
As a last resort, sender verification can be disabled on the provider side.
Error #5: Too Many Requests
Error Message
“Too Many Requests.”
Cause
Too many emails were sent at the same time, exceeding provider limits.
How to Fix
Contact Kyrios support.
Limits can be adjusted or sending optimized on the backend.
Error #6: 421 Temporary System Problem (Google Workspace)
Error Message
421 4.3.0 Temporary System Problem. Try again later
Cause
Google Workspace temporarily rejected the email due to system load or rate limiting.
[Screenshot: 1764181604185-3.png]
How to Fix
Send emails using drip mode instead of bulk sending.
Reduce send volume and spacing between messages.
Common Issues and Fixes
DNS shows verified but emails still fail: Click Verify DNS Settings again in Mailgun.
Red triangle icon appears: Indicates a permanent or hard failure. The email will not resend automatically.
Fix applied but email not sent: You must manually resend the email or restart the workflow.
FAQ
Why is my domain not allowed to send emails through Mailgun?
This happens when the domain is unverified or DNS records are incomplete. Verify all required DNS records in Mailgun and refresh verification if needed.
What should I do if my Mailgun account shows “Account Terminated”?
Contact Kyrios support. Kyrios will coordinate with the Mailgun team to identify the reason and resolution.
How do I fix sender verification errors?
Ensure MX records are set to Mailgun for the sending domain and that the From address matches the sending domain exactly.
What does “Too Many Requests” mean?
It means the email provider rate-limited your account due to high send volume. Kyrios support can adjust sending behavior.
Will Kyrios automatically retry failed emails?
No. Permanent failures must be resent manually after the issue is resolved.
What does the “Too old” error mean?
The message expired before delivery. Contact Mailgun support for investigation.
My DNS records show green checkmarks, but the error persists. Why?
DNS records may not be fully propagated or refreshed. Click Verify DNS Settings again to update the status.