Hi All, we are not able to send emails to one of the domain address (Ex: *.xxx.co.uk). as result, senders are getting NDR with SPF validation error but when I refer to message details it is saying "The message was rejected because of Sender Policy Framework violation -> 550 DMARC Sender Invalid - envelope rejected". below are more details. further, I can confirm recipient is enabled DMARC from their end and we aren't enabled at this point. I have checked the SPF record validation via MX toolbox and it has also been fine. appreciate the help here. Thanks, Dilan

Hi @Dilan Nanayakkara According to your information above, you are using Exchange online (cloud only?) sending mails to (all?) the users in the specific domain(*.xxx.co.uk) failed, correct me if I have any misunderstadings. Could you please provide the complete NDR message you received? And according to the Error code DMARC Sender Invalid and introduction in this link: Mimecast SMTP Error Codes Please ensure all the IP address for your mail servers are listed in your SPF records, for the configuration of SPF in O365, referring to the official document: Set up SPF to help prevent spoofing If an Answer is helpful, please click " Accept Answer " and upvote it. Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Unable to send emails on a specific domain - 550 DMARC Sender Invalid - envelope rejected

Accepted answer

Joyce Shen - MSFT 16,641 Reputation points

2020-12-10T02:48:58.703+00:00

Hi @Dilan Nanayakkara

According to your information above, you are using Exchange online (cloud only?) sending mails to (all?) the users in the specific domain(*.xxx.co.uk) failed, correct me if I have any misunderstadings.

Could you please provide the complete NDR message you received?

And according to the Error code DMARC Sender Invalid and introduction in this link: Mimecast SMTP Error Codes

Please ensure all the IP address for your mail servers are listed in your SPF records, for the configuration of SPF in O365, referring to the official document: Set up SPF to help prevent spoofing

If an Answer is helpful, please click "Accept Answer" and upvote it.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.
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Dilan Nanayakkara 1,111 Reputation points

2020-12-10T03:29:07.273+00:00

@Joyce Shen - MSFT Thanks for the replying,

Yes, cloud-only. as per latest troubleshoot, we are able to send a just normal email to *.xxx.co.uk but if we are forwarding like meeting invitation on behalf of, it will be failed, I believe blocked at their side due to DMARC – the invite appeared as the organizer but sent from a different address.

So as a troubleshooting step, I have recreated the invite and sending it across then it has succeeded.

However, as part of troubleshooting, I have analyzed the message header and found out SPF has failed, Please refer the below image. but when I have checked just only SPF record on MX toolbox, there were no errors.

this might not be the case of delivery failure but appreciate your help on how to correct the failed SPF record here.

Thanks,
Dilan

Joyce Shen - MSFT 16,641 Reputation points

2020-12-11T08:29:54.45+00:00

Hi @Dilan Nanayakkara

Thanks for sharing further information above, are the delegator and sender in the same domain?

What about forwarding normal emails rather than meeting invitation? Or try forwarding the invitation as attachment?

And the introduction for Use DMARC to validate email

I also found a link which discussed about this issue: Calendar invites forwarded by Outlook violate DMARC

If the domain of the meeting organizer has an enforced DMARC policy (i.e. p=quarantine, or p=reject), and the recipient mail server honors DMARC, the message will not be delivered, because DMARC does not allow an unauthorized mail server (i.e. the forwarding mail server) to send an email as the organizer’s domain.

Joyce Shen - MSFT 16,641 Reputation points

2020-12-18T00:58:04.11+00:00

Hi @Dilan Nanayakkara

Any update about your issue?
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Unable to send emails on a specific domain - 550 DMARC Sender Invalid - envelope rejected

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