Non-Delivery Report: [501.5.1.8 Your message couldn't be delivered because the email has no mail from address]

Before you start working on the resolution for the NDR group or an individual user, make sure you have: 
Installed Online PowerShell V2 module
Connected to Exchange Online

Install Exchange Online PowerShell V2 module: 

1. Open the Windows PowerShell and run this command as an Administrator:
   
   Install-Module -Name ExchangeOnlineManagement
2. Confirm that you want to install this PowerShell module. NOTE: For additional installation options, see ExchangeOnlineManagement.

Connect to Exchange Online: 

• If you have Multi-Factor Authentication enabled, run this command:
  
  Connect-ExchangeOnline -UserPrincipalName <UPN> -ShowProgress $true
  In <UPN> enter your username.
  
  
• If you don't have Multi-Factor Authentication enabled, run this command:
  
  Connect-ExchangeOnline -Credential $UserCredential -ShowProgress $true
  
  When prompted, enter your password (and the Multi-Factor Authentication verification code if required).
  
  Once you have successfully installed the Exchange Online PowerShell module and connected to Exchange Online, please see what you need to do next if the email is sent to a group and if the email is sent to an individual user.

This issue occurs when there is no sender specified in the message envelope. If the sender is blank, Signatures for Microsft 365 cannot identify the tenant to append for the email signature. 

• If no on-premise Active Directory exists, then amend the distribution group properties in Microsoft 365 using Windows PowerShell.
  
  NOTE: Please ensure that Windows PowerShell is connected to Microsoft 365 before running the following commands.
  To do this, check the Pre-requisites section of this guide.
  To complete the steps described below, you will need:
  Microsoft 365 Global Administrator credentials
  
  Amending the distribution group properties:

1. Run the following command:
   
   Get-DistributionGroup <Group Email Address> | fl *ReportToOriginatorEnabled*
2. If the value returned is False then run this command to change it to True: 
   
   Set-DistributionGroup <Group Email Address> -ReportToOriginatorEnabled $true

• If an on-premise Active Directory exists and the distribution group is synchronized to Microsoft 365, then: 
  
  From the distribution group Properties, set the attribute ReportToOriginator to TRUE.
  
  These changes will not take effect until the on-premises Active Directory domain has been synchronized and replicated in Microsoft 365.

According to Microsoft, "Any mail to JournalingReportNdrTo mailbox will not be journaled and it will not honor transport and mailbox rules settings. It is recommended to create a dedicated mailbox for JournalingReportNdrTo setting or set it to an external address."

For more information, see Transport and mailbox rules in Exchange Online or in on-premises Exchange Server don't work as expected.

• Specify a dedicated mailbox, as the recipient for Journal Report NDR messages, in Microsoft 365 using Windows Powershell.
  
  NOTE: Please ensure that Windows PowerShell is connected to Microsoft 365 before running the following commands.
  To do this, check the Pre-requisites section of this guide.
  To complete the steps described below, you will need:
  Microsoft 365 Global Administrator credentials

  
  Specifying a dedicated mailbox:
  

  Run the following command:  

  set-transportconfig -JournalingReportNdrTo <insert mailbox address>
  Tip! Microsoft recommends that the JournalingReportNdrTo recipient be set to an external email address or a dedicated mailbox created, which has no transport or mailbox rules applied.