For security purposes, a number of attachment types are blocked by default by Microsoft Office 365. These types are those where the risk of malicious content is significant - and the legitimate use of the file types are limited. The list of attachment types are below. They are subject to change without notice as risk conditions warrant.
Microsoft Office - Macro Enabled File Types
- .docm, (Word)
- .ppsm, .pptm .sldm (Powerpoint)
- .xlam, .xlm (Excel)
Executable Content Types:
- .com
- .dll
- .dos
- .exe
- .jar
- .obj
- .os2
- .pif
- .rar
- .vbe
- .vxd
- .w16
Other file types:
- .ace (extremely uncommon compressed file type)
- .ani
- .app
- .reg (Microsoft Registry File)
- .w16