What is the error "550 5.1.8 Access denied, bad outbound sender"?


When sending an email message you may receive a Non-Delivery Report (NDR), also known as a "bound message", that has this information displayed:

Delivery has failed to these recipients or groups:

Your message couldn't be delivered because you weren't recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it's no longer allowed to send email. Contact your email admin for assistance.

There will be addition information in the "Diagnostic information for administrators"

Remote Server returned '550 5.1.8 Access denied, bad outbound sender AS(42004)'

Here is an example message in Outlook web:



The university restricts outbound email delivery to 50 recipients per-hour and 250 recipients per-day.

  • If you are sending a message to a small number of recipients you may have hit the per-hour recipient limit
    • Action: Wait 1 hour before re-sending the message.
  • If you are attempting to send a mass mailing, or send to a large email group, you may have hit both the per-hour and per-day sending limits.
    • Action: Wait 1 hour and resend to a portion of your list or Contact University Communications and Marketing for bulk-mail delivery assistance.





Article ID: 2233
Fri 7/22/22 11:08 AM
Mon 7/25/22 7:37 PM