Undeliverable Message email

Question

I have received hundreds of "Undeliverable Message" emails since we started Office 365.  None of the emails listed as sender are real emails.  How is this happening?  We never had an issue like this when we had our own Exchange Server.

Answer 1

Hi adminQuecheeClub,

We need to collect the entire error message “Undeliverable Message” for further analysis. To protect your privacy, can you send it to us via this link: https://answers.microsoft.com/en-us/privatemessages/list

Since you mentioned that you have on-premises Exchange Server, do you have a hybrid deployed in your organization? If yes, please share more information about your mail routing.

To better understand your situation, I’d like the confirm the following information:

1. Are these emails sent to a specific domain or all external recipients?
2. Can you receive the email sent from the same recipients as expected when you cannot send the email to them?
3. How do you send and receive emails, via Outlook client or OWA(Outlook Web App) or other mail clients? If it’s not OWA, please try sending the email in OWA to see if the issue persists.

Thanks,

Rick

Answer 2

Hi Alan Emery,

Thanks for your PM reply.

Did you configure the notification setting?

Also, please make sure the option “ SPF record: hard fail “ is turned on(Protection>Spam filter> advanced options).

Regards,

Rick

Answer 3

Hi Rick,

I had it set for both internal and external, but changed it to internal only months ago, which is why I am concerned as to how these emails are being sent.  Whatever, or whoever, is trying to send these emails out, they are using our domain "quecheeclub.com" to do so.  Each one has malware attached.  What I am not sure of is if this is being done from the cloud side or from the domain side.

I turned on the SPF filter.

Thanks for your response,

Alan

Answer 4

Hi Alan,

That’s the reason why you receive hundreds of “Undeliverable Message” emails, which were created automatically by mail delivery software. Since you had it set for both internal and external senders, you will get this notification message once someone triggers the malware policy.  

Don’t worry about this. If you want to know more information about Exchange Online Protection, you may refer to this link: https://technet.microsoft.com/en-us/library/jj723137(v=exchg.150).aspx

Regards,

Rick

Answer 5

Hi Rick,

I have replied three times to your private message.  Hope to find a resolve soon.

Sincerely,

Alan