The default email file name format used when saving emails with the MacroView Mail App ensures each email has a unique name and prevents duplication of emails within any single location in SharePoint Online (Office 365).
MacroView Mail will identify the email as a duplicate when it is being saved by different users and prevent them from re-saving it with the same file name in the same location.
It is still possible however to change the filename on the properties page when saving an email or to save the same message to a different location.
The default File name format is:
This format results in a unique name for each email, as the SentOn placeholder is substituted with the date and time the email was sent to the second.
All emails saved using MacroView Mail are saved in EML format which preserves the original email and any attachments.