How to fix Access Denied / Bad outbound sender error while sending an email?

You might receive a non-delivery report when you send an email. The error details are as below:

550 5.1.8 Access denied, bad outbound sender AS (41000001)
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 messages outside of your organization. Contact your email admin for assistance.


When an email address is identified as spam, that user's email address is added to the blocked sender's list, resulting in the above error. The Office 365 plan has a limit set for sending emails to the maximum number of recipients, and this issue can occur if emails are sent to a large number of recipients that exceed this limit. Refer to this link for more details.

  1. Navigate to restricted users in the Office 365 Security and Compliance center from this direct link -
  2. Now you will get the restricted users list. Choose the specific user for which you need to revoke the restriction.
  3. Then choose Unblock.


Streamline Email Signature Management with a Free On-demand Demo from Sigsync

Sigsync email signature service provides effortless, centralized signature management for Office 365 and Exchange. Our team can assist you in quickly setting up company-wide signatures. Request a free on-demand demo to see how Sigsync can simplify your email signature management process.


Demo sitemap