Hi Www_w_,

There are several causes why users receive NDR when sending emails. NDRs include a code that indicates why your email isn’t delivered, you can refer to the list in this article.

In your case, the emails you send have an invalid sender address (null sender), so it would be rejected by Office 365. Sometimes a rejected message will appear as “550 5.7.512 Access denied, message must be RFC 5322 section 3.6.2 compliant and include a valid From address”. This is an expected behavior, as the NDR cannot be sent back to the sender whose address is invalid. Therefore, NDR will not be sent and it will be “discarded”

We appreciate your understanding and patience. 

Best Regards,

Ruel

Hi Miles Taylor,

The "(null) (null)" you're seeing in the From field is the display name your contact's Yahoo account is sending out. Yahoo builds the sender's display name from the First name and Last name fields on their Yahoo profile. When those two fields are blank or weren't saved properly, Yahoo literally sends the name as "(null) (null)" in the email header. Outlook is simply showing what Yahoo provides.

This is why his name appears correctly when you email him (Outlook is using the name saved in your Contacts), but when he replies, Outlook displays the broken name his Yahoo account is sending.

Here are the steps your contact needs to do this on his Yahoo account:

1. Sign in to Yahoo Mail on a desktop browser at mail.yahoo.com.
2. Click the Settings gear (top right) > More Settings > Mailboxes.
3. Select his Yahoo mailbox under "Mailbox list".
4. Under Your name, make sure both the First name and Last name fields are filled in correctly (not blank, no special characters).
5. Click Save.
6. He should also check the Personal info in the Yahoo account page and confirm the first/last name fields there are populated and saved.
7. Sign out fully and sign back in, then send you a fresh test email.

If the fields already look correct, ask him to clear them, save, then re-enter them and save again. That re-write is often what clears the underlying null value.

While he sorts that out, you can override the display in Outlook so his replies show his real name:

1. Open one of his replies in Outlook.
2. Right-click his "(null) (null)" name at the top of the message > Edit Contact (or open his entry in People).
3. In the Display as / File as field, type his real name.
4. Save.

Outlook will then use that name for incoming messages from his address, even while Yahoo keeps sending the broken header.

Please let me know how it goes after he updates his Yahoo profile, I will be happy to help further if it sticks around.

Kind regards,

P/S: Since this is a public forum, I have edited and removed personally identifiable information from post to protect your privacy. The next time you post, it is safer to hide your personal information in the posts beforehand.

Sender related properties are only set after the message is actually sent. Try to use the Items.ItemAdd event on the Sent Items folder (retrieved using Namespace.GetDefaultFolder).

If SendUsingAccount property is not set, you can assume the default account is being used - use the first account from the Namespace.Accounts collection and retrieve the Account.SmtpAddress property.