Unable to open secured email .msg file more than once that saved on desktop

Hi,

I had XXX add-in that sign & encrypted emails (the secured email will be embedded with a lock and attachment icon) and also had SEP Outlook Add-in in the Microsoft Oulook.

I had issue opening secured email (.msg) file more than once that was saved on the desktop. Error message prompted "We can't open 'Path Directory\XXX.msg' It's possible the file is already open, or you don't have permission to open it. To check your permissions, right-click the file folder, then click Properties."

However, I had no issue opening secured emails in Microsoft Outlook pst and ost, but only .msg file saved in desktop. Previously without the SEP Outlook Add-in, we does not encountered the issue too.

My vendor claimed that SEP Outlook Add-in was not doing anything to the secured emails saved on desktop as SEP Outlook Auto-Protect was not enabled, thus it will not be scanning emails and attachments if any. Is this correct?

Based on the testing we conducted as shown in the table below, the secured email was able to open more than once after disabling the SEP Outlook add-in. If SEP Outlook add-in was enabled, the secure email will not be able to open more than once with encountered error message unless we modified the file attributes to "Read-Only", then we will be able to open more than once successfully. In scenarios 1 & 2, XXX add-in was enabled and the difference lies on SEP outlook add-in. 

My claim was when SEP Outlook add-in was enabled, user only need to modified the file as read-only to make SEP Outlook Add-in believe that there is no modification of the secured email (Saved on Desktop). Restart Outlook, SEP Outlook Add-in scanned and discovered that the secured email will not be able to modify and allowed the file to be open more than once. Is my understanding correct?

What does SEP Outlook Add-in do? Attachment scanning and Auto Protect?

Does SEP Outlook Add-in do attachment scanning on .msg files saved on desktop? Even when SEP Outlook Auto-Protect was not enabled? 

Note: We should not be disabling XXX add-in as it will defeat the purposed of the secured email. When we disable XXX add-in, the secured email is no longer consider as a secured email but as a blank email.

Thanks and Regards,

Ash