Email delivery status notification with MailKit/Mimekit

Question

Email delivery status notification with MailKit/Mimekit

Dharmaraj Kurle 20

Hello,

We are successfully sending emails to our partner organization, which is hosted on Office 365. The partner has configured an incoming Mail Flow Connector and corresponding rule to allow emails from our domain.

We're using MailKit within our .NET Core application to send these emails. However, the delivery status we receive is always marked as successful, regardless of the actual delivery outcome.

We would like to know how to detect failed deliveries in the following scenarios:

The recipient email address does not exist in the partner's Office 365 tenant.

The email is rejected due to Mail Flow rule restrictions configured at the partner’s end.

Any other delivery failures.

Your guidance on how to capture or monitor such failures would be greatly appreciated.

Thank you in advance.

Accepted answer

0 additional answers

Your answer

Answer 1

Jack-Bu 2,610 Microsoft External Staff Moderator

Hi @Dharmaraj Kurle,

Thanks for reaching out to the Microsoft Q&A forum.

Based on your inquiry, I understand you're looking to detect failed email deliveries when sending mail using Mailkit/MimeKit. While this specific scenario, involving a third-party product, falls outside the direct scope of general Microsoft support, our mission is always to help you find the best possible solution. Therefore, I've gathered some resources that I believe will be beneficial.

Message trace is an incredibly helpful tool for thoroughly investigating email messages as they pass through your Microsoft 365 tenant. It can help you determine why a message might have been rejected, whether due to a mail flow rule, an invalid recipient email address, or other factors. For a detailed explanation, please refer to this article: Message trace in the new EAC in Exchange Online | Microsoft Learn.

You mentioned that your partner has set up a mail flow connector with security restrictions, and emails sent always appear successful despite the actual outcome. I recommend reviewing the configuration in your partner's tenant using this article as a guide: Set up connectors for secure mail flow with a partner organization in Exchange Online | Microsoft Learn.

We understand how crucial reliable email delivery is for your operations. If you encounter any issues or have further questions, please don't hesitate to reply to my answer once you have any replies/updates.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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.

Dharmaraj Kurle 20 Reputation points

2025-06-19T06:41:23.78+00:00

Hi @Jack-Bu ,

Thank you for your response.

While Message Trace is helpful in identifying the root cause of email delivery issues, it is a time-consuming process and requires manual effort.

Our primary goal is to determine whether an email was successfully delivered or not in real time—understanding the root cause of failure is not critical in our case.

Could you please suggest any options or approaches to achieve this?
Vergil-V 1,955 Reputation points Microsoft External Staff Moderator

2025-06-20T13:52:06.4+00:00

Hi Dharmaraj Kurle
I truly appreciate your patience, and I'm glad to provide you with clear information on this topic.

By design, an email needs to pass through four layers of Exchange Online Protection (EOP) before it reaches the recipient's mailbox.

Each of these layers performs different actions, such as: Quarantining the message; rejecting the message with a non-delivery receipt (NDR); sending it to the Junk folder; …. These actions are triggered when a message matches specific policies within EOP.

For more detailed information, you can refer to the following Microsoft documentation: Exchange Online Protection (EOP) overview - Microsoft Defender for Office 365 | Microsoft Learn

With that said, as the sender, you might receive an NDR, or you may not receive any information regarding the success of the email delivery. In that case, you could ask the recipient to check their quarantine or junk folder to verify whether the message was delivered successfully or not.

For further information regarding the status of message notifications, we recommend reaching out to Mailkit/Meilkit support directly.

I hope this clarifies how to determine whether an email was successfully delivered in real-time. If you encounter any issues or have further questions, please don't hesitate to reach out.
Vergil-V 1,955 Reputation points Microsoft External Staff Moderator

2025-06-23T07:27:02.1566667+00:00

Hi Dharmaraj Kurle,

I hope you're doing well. I just wanted to kindly check in and see if there have been any updates regarding the information I shared about determining whether an email was successfully delivered in real-time.
Have you had a chance to review my response so far?

I’d appreciate any updates you can provide, and please let me know if there’s anything further I can do to assist.

Thank you for your understanding!
Vergil-V 1,955 Reputation points Microsoft External Staff Moderator

2025-06-25T09:45:40.4033333+00:00

Hi Dharmaraj Kurle,
I hope this message finds you well.
I wanted to kindly follow up, as it's been a little while since we last touched base regarding the information I shared about monitoring real-time email delivery status.
If your question has been answered, please consider marking the helpful replies as solutions. This really helps others in the community find the support they need more easily.
Thank you for your time and understanding.

Share via

Email delivery status notification with MailKit/Mimekit

0 additional answers

Your answer