Distribution mailbox is almost full, cannot find any members of that distribution list to be storage almost full.

Hi @Amirul Hafeez Bin Johan

Thank you for the detailed information. I completely understand how frustrating this has been for you, and you’ve already done an excellent job of troubleshooting. 

You are absolutely right that a standard distribution list doesn't have a mailbox. Your finding that none of the members' mailboxes are full is the most important clue. This suggests that the “mailbox full” warning isn’t for an individual member, but rather for a separate mailbox associated with the group itself. 

In Microsoft 365, it's possible for a group that appears to be a distribution list to actually be a different type of object behind the scenes, such as a Microsoft 365 Group, a Mail-enabled Security Group, or even a Shared Mailbox using the same email alias. These types do have actual mailboxes, which could be the source of the warnings. 

To move forward, I suggest checking the actual group type. The most reliable place to do this is in the Microsoft Entra admin center: 

• Log into the Microsoft Entra admin center. 
• Go to Groups > All groups. 
• Find the group giving you the alert and look for the Group type column. This will show whether it's a Distribution list, a Microsoft 365 group, or a Security group. 

Once you confirm the group type, we can take the next appropriate steps: 

• If it's a Microsoft 365 Group or Shared Mailbox, you can review its mailbox usage in the admin portal and clean up old items or adjust the storage quota if needed. 
• If it's truly a distribution list, we may need to investigate further; for example, whether the DL address is linked to another object, or if mail flow rules, journaling, or alias conflicts might be involved. 

Please know that while this response may not fully resolve the issue just yet, your input is incredibly valuable. With this additional detail, we’ll be able to move forward more accurately. 

If you need help interpreting what you find, just reply here. I’ll be happy to take a closer look and guide you through the next steps toward a full resolution. 

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