Outlook receiving read receipt continuosly from old emails

Question

So this is the scenario. 2 of our employees suddenly receive a bombarded read receipts daily from old receipts. Can anyone help find this issue's problem or does anyone know how to fix it? I've been investigating this issue for a week now.

Thank you in advance.

Answer 1

@Karl Soriano

Before troubleshooting, I would suggest you create a transport rule to block those emails first:

1. Create this old email address as mail contact (If this mailbox still exist on your Exchange server, you could bypass this step).
2. You will could create a transport rule to block emails which sent from this old email address.

About this issue, I would suggest you use message tracking log to check how this email generated.

Get-TransportService | Get-MessageTrackingLog -Sender UserA@domain.com -Recipients UserB@externaldomain.com -MessageSubject "Test2"   

You can also try to open this old mailbox to check whether there exist unread emails in that mailbox. Those read receipt may caused some other user read emails for this mailbox.

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