NDR Messages getting rejected

Question

Hi,

im getting this strange error from one of my clinet.

"host techoneglobal-com.mail.protection.outlook.com[52.101.132.30] said: 501 5.1.7 Invalid address [HK3PEPF0000021A.apcprd03.prod.outlook.com 2024-05-07T09:24:38.125Z 08DC6DF45E00D1A9] (in reply to MAIL FROM command)"

Any one know how to resolve?

BR

Answer 1

Hi Kanchana Jayathilake，

Welcome to the Microsoft forum.

I would like to know if your organization is using Exchange Online or Exchange Server? Is the sender of this email an Exchange Online user or an Exchange Server user? Is the recipient of this email an Exchange Online user or an Exchange Server user?

Based on my experience , usually the cause of this error is that the sender's email address is incorrect. You can start by checking the format of the email address in the FROM section of the message. Please note that it should be the full e-mail address e.g. user1@domain.com, not an alias e.g. user1. If the sender's email address does not have any formatting as well as spelling errors, you can also try the following:

• Remove the recipient's email address from your Auto-Complete list.
• Confirm that the recipient isn't auto-forwarding messages from you to another (and likely, invalid) email address.
• Verify that your account hasn't been compromised.
• Confirm that the NDR is related to a message that you actually sent.

About the details you can refer to : Fix NDR error 550 5.1.1 through 5.1.20 in Exchange Online - Exchange | Microsoft Learn.

I hope this helps. Any updates please be free to contact me.