Unable to send emails via Outlook Mail API - Says message could not be delivered

Manish Narayan 1 Reputation point

Hello, We have a product that uses Outlook Mail API to help our customers in sending emails.
We use the Outlook Mail API to sync emails and send emails for any user.

We have one particular client who are not able to send any emails from their account.
The email we are trying to send from belongs to - ap@xyz .com

When they try to send emails from our application to any email like - simon@xyz .com Outlook is responding with a bounce message saying - 'Your message to simon@xyz .com could not be delivered. simon was not found at xyz.com .

More Info that we get from the message -

More Info for Email Admins
Status code: 550 5.1.10

This error occurs because the sender sent a message to an email address hosted by Office 365 but the address is incorrect or doesn't exist at the destination domain. The error is reported by the recipient domain's email server, but most often it must be fixed by the person who sent the message. If the steps in the How to Fix It section above don't fix the problem, and you're the email admin for the recipient, try one or more of the following:

The email address exists and is correct - Confirm that the recipient address exists, is correct, and is accepting messages.

Synchronize your directories - If you have a hybrid environment and are using directory synchronization make sure the recipient's email address is synced correctly in both Office 365 and in your on-premises directory.

Errant forwarding rule - Check for forwarding rules that aren't behaving as expected. Forwarding can be set up by an admin via mail flow rules or mailbox forwarding address settings, or by the recipient via the Inbox Rules feature.

Recipient has a valid license - Make sure the recipient has an Office 365 license assigned to them. The recipient's email admin can use the Office 365 admin center to assign a license (Users > Active Users > select the recipient > Assigned License > Edit).

Mail flow settings and MX records are not correct - Misconfigured mail flow or MX record settings can cause this error. Check your Office 365 mail flow settings to make sure your domain and any mail flow connectors are set up correctly. Also, work with your domain registrar to make sure the MX records for your domain are configured correctly.

What we confirmed from the user is that they are able to send emails when they do it directly from their outlook accounts, but when we try do the same with the outlook mail API we are being responded with the above undeliverable error.

Is there any way this would only happen when we make the API calls? How can I go about getting this fixed for our customer?

Thank you

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  1. Srinivasa Rao Darna 6,701 Reputation points Microsoft Vendor

    Hi @Manish Narayan ,

    If you get a non-delivery report (NDR), also called a bounce message, for error code 550 5.1.10, this article can help you fix the problem and get your message sent.


    You can also raise a support case with Microsoft, a specialized Support Engineer will be able to assist you better.

    You can raise technical support request from:
    https://portal.azure.com/#view/Microsoft_Azure_Support/HelpAndSupportBlade/~/overview or https://admin.microsoft.com/#/support/requests.

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

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