An mau file extension is related to the Media Attachment Unit file format.
MAU file extension - Media Attachment Unit data
What is mau file? How to open mau files?
The mau file extension is used for a special executable format called Media Attachment Unit Format.
Most likely used in the past for some sort of attachment. Seems to be obsolete.
This mau file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.