What are the file types that are blocked in Outlook?

The current list follows. For details, see this Microsoft article.

.ade
Access Project Extension (Microsoft)

.adp
Access Project (Microsoft)

.app
Executable Application

.asp
Active Server Page

.bas
BASIC Source Code

.bat
Batch Processing

.cer
Internet Security Certificate File

.chm
Compiled HTML Help

.cmd
DOS CP/M Command File, Command File for Windows NT

.com
Command

.cpl
Windows Control Panel Extension (Microsoft)

.crt
Certificate File

.csh
csh Script

.der
DER Encoded X509 Certificate File

.exe
Executable File

.fxp
FoxPro Compiled Source (Microsoft)

.gadget
Windows Vista gadget

.hlp
Windows Help File

.hta
Hypertext Application

.inf
Information or Setup File

.ins
IIS Internet Communications Settings (Microsoft)

.isp
IIS Internet Service Provider Settings (Microsoft)

.its
Internet Document Set, Internet Translation

.js
JavaScript Source Code

.jse
JScript Encoded Script File

.ksh
UNIX Shell Script

.lnk
Windows Shortcut File

.mad
Access Module Shortcut (Microsoft)

.maf
Access (Microsoft)

.mag
Access Diagram Shortcut (Microsoft)

.mam
Access Macro Shortcut (Microsoft)

.maq
Access Query Shortcut (Microsoft)

.mar
Access Report Shortcut (Microsoft)

.mas
Access Stored Procedures (Microsoft)

.mat
Access Table Shortcut (Microsoft)

.mau
Media Attachment Unit

.mav
Access View Shortcut (Microsoft)

.maw
Access Data Access Page (Microsoft)

.mda
Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)

.mdb
Access Application (Microsoft), MDB Access Database (Microsoft)

.mde
Access MDE Database File (Microsoft)

.mdt
Access Add-in Data (Microsoft)

.mdw
Access Workgroup Information (Microsoft)

.mdz
Access Wizard Template (Microsoft)

.msc
Microsoft Management Console Snap-in Control File (Microsoft)

.msh
Microsoft Shell

.msh1
Microsoft Shell

.msh2
Microsoft Shell

.mshxml
Microsoft Shell

.msh1xml
Microsoft Shell

.msh2xml
Microsoft Shell

.msi
Windows Installer File (Microsoft)

.msp
Windows Installer Update

.mst
Windows SDK Setup Transform Script

.ops
Office Profile Settings File

.pcd
Visual Test (Microsoft)

.pif
Windows Program Information File (Microsoft)

.plg
Developer Studio Build Log

.prf
Windows System File

.prg
Program File

.pst
MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)

.reg
Registration Information/Key for W95/98, Registry Data File

.scf
Windows Explorer Command

.scr
Windows Screen Saver

.sct
Windows Script Component, Foxpro Screen (Microsoft)

.shb
Windows Shortcut into a Document

.shs
Shell Scrap Object File

.ps1
Windows PowerShell

.ps1xml
Windows PowerShell

.ps2
Windows PowerShell

.ps2xml
Windows PowerShell

.psc1
Windows PowerShell

.psc2
Windows PowerShell

.tmp
Temporary File/Folder

.url
Internet Location

.vb
VBScript File or Any VisualBasic Source

.vbe
VBScript Encoded Script File

.vbs
VBScript Script File, Visual Basic for Applications Script

.vsmacros
Visual Studio .NET Binary-based Macro Project (Microsoft)

.vsw
Visio Workspace File (Microsoft)

.ws
Windows Script File

.wsc
Windows Script Component

.wsf
Windows Script File

.wsh
Windows Script Host Settings File

.xnk
Exchange Public Folder Shortcu