Hi @GK-6729,
What's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
The problem only occurs when the attachment is created in BI Publisher not with regular emails.
According to your description, seems that the key of your issue might be here. Please kindly forgive me not know much about the "BI Publisher" you mentioned here.
So, how did you create new email message and add the specific attachment? Via Outlook desktop client, "New Email" and "Attach File" to select the specific attachment file made from BI Publisher? Or those operations are all finished in your BI Publisher?
Any update, please feel free to post back.
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