My emails won’t send saying it’s likely scam, (not scam )

Question

Hi I got this email,

This message couldn't be delivered because the sending email address was not recognized as a valid sender. The most common reason for this error is that the email address is, or was, suspected of sending spam. Contact the organization's email admin for help and give them this error message.

Diagnostic information for administrators:

Generating server: [Moderator note: personal info removed]

[Moderator note: personal info removed] Remote server returned '550 5.1.8 Access denied, bad outbound sender AS(42004)'

Original message headers:

Received: from 
and the person I am emailing is not a scam please help fix this! Thanks! 

Answer 1

The error 550 5.1.8 Access denied, bad outbound sender means the sending account has been blocked because it exceeded Exchange Online sending limits or was (or is) suspected of sending spam.

To fix this:

1. If this is a school or organization account (for example @carlislestudents.org):
   • Contact the school/organization’s email administrator and provide the full error text, including 550 5.1.8 Access denied, bad outbound sender AS(42004).
   • The admin should:
     1. Check whether the account is or was compromised and follow the steps in Secure a compromised email account in Exchange Online.
     2. Go to the Microsoft 365 Defender portal → Restricted entities page and unblock the user account.
     3. Wait up to about an hour for restrictions to clear, then try sending again.
2. As the mailbox owner:
   • Review Sent Items for messages not sent by the user. If anything looks suspicious, report it to the admin and follow the guidance to determine whether the account is compromised.
   • After the admin unblocks the account, send a test email to confirm mail flow is restored.

The issue is not about the specific person being emailed; it is about the sending account being temporarily blocked due to spam-related limits or suspicion.

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References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"

Answer 2

Thank uuuu