Please try the following step :-

To disable the plug-in from the Symantec Endpoint Protection Manager (SEPM):

• 1. Open up the AV policy in SEPM.
  2. Click on Microsoft Outlook Auto-Protect
  3. Unselect Enable Microsoft Outlook Auto-Protect

To disable the plug-in from within the Symantec Endpoint Protection (SEP) client interface:

• 1. Open up the SEP client UI.
  2. On the AV bar, click Options and then click Change Settings...
  3. Click on Outlook Auto-Protect
  4. Unselect Enable Microsoft Outlook Auto-Protect

To disable the plug-in from Outlook:

• 1. Open Outlook
  2. Click Tools -> Options
  3. Select the Other tab
  4. Click the Advanced Options button
  5. Click the Add-in Manager button
  6. Unselect the Symantec AntiVirus Outlook Protection

Please reply with status update!

Cheers!!

From your SEPM, you can open AV policy in SEPM, and goto Microsoft Outlook Auto-Protect tab.

I suspect that the attachment is being detected as a threat. Or you have enabled scanning of compressed file and the attachment is a password protected compressed file.

In later case you can disable scanning of compressed files by deselecting the option 'Scan files inside compressed files'.

You can also goto Actions tab, and for Malware/SecurityRisks change the default action from 'Clean Risk' to 'Quarantine' or 'Log only'. But in this case you need to monitor the logs for suspicious attachments.

Alternatively, if you know the extension, you can exclude that extension from being scanned.

Note of caution - If you take any of these actions you are in effect reducing the Outlook protection. So please monitor the logs and setup carefully.