How to fix Delivery has failed to these recipients or groups

Question

I have tried to send email for a company and a person which isn't the first-time sending emails to each other but recently when I try to send emails back to them, I mails bounces back and show the below message. knowing that we have sent emails to each other a lot and now I can't anymore. i couldn't find any solution on internet too please need help urgent

The address you sent your message to wasn't found at the destination domain. It might be misspelled or it might not exist. Try to fix the problem by doing one or more of the following:

1. Send the message again, but before you do, delete and retype the address. If your email program automatically suggests an address to use, don't select it.
2. Clear the recipient AutoComplete cache in your email program by following the steps in this article: <Mod repair URL>Status code 5.1.1. Then resend the message, but before you do, be sure to delete and retype the address.
3. Contact the recipient by some other means (by phone, for example) to confirm you're using the right address. Ask them if they've set up an email forwarding rule that could be forwarding your message to an incorrect address.

Answer 1

Hi,@mohamed omar

Thanks for posting your question in the Microsoft Q&A forum.

Based on your description, you seem to be experiencing a failure to send emails.

Did you get your problem solved? Did you try any of these methods you provided? If the problem persists, please refer to the suggestions below:

1.Try using another email address to send an email to that address to confirm if you have the same problem.

2.Please provide a complete screenshot of the NDR to make it easier to analyze the cause of the error.