We are silently blocking nearly all attachment types classified as unsafe in Microsoft Knowledge Base Article - 262631 with the exception of Access database files (extension of mdb). This list to be blocked includes:

Extension       File type
---------------------------------------------------
.app            Visual FoxPro Application 
.ade            Microsoft Access project extension 
.adp            Microsoft Access project 
.ani            Animated Icon 
.asx            Windows Media Audio / Video
.bas            Microsoft Visual Basic class module 
.bat            Batch file 
.chm            Compiled HTML Help file 
.cmd            Microsoft Windows NT Command script 
.com            Microsoft MS-DOS program 
.cpl            Control Panel extension 
.crt            Security certificate 
.cur            Animated Icon 
.csh            Unix shell extension 
.exe            Program 
.fxp            Visual FoxPro Compiled Program 
.hlp            Help file 
.hta            HTML program
.ico            Animated Icon 
.inf            Setup Information 
.ins            Internet Naming Service 
.isp            Internet Communication settings 
.js             JScript file 
.jse            Jscript Encoded Script file 
.ksh            Unix shell extension 
.lnk            Shortcut 
.mda            Microsoft Access add-in program 
.mde            Microsoft Access MDE database 
.mdt            Microsoft Access workgroup information  
.mdw            Microsoft Access workgroup information 
.mdz            Microsoft Access wizard program 
.msc            Microsoft Common Console document 
.msi            Microsoft Windows Installer package 
.msp            Microsoft Windows Installer patch 
.mst            Microsoft Windows Installer transform; 
Microsoft Visual Test source file 
.ops            Office XP settings 
.pcd            Photo CD image; Microsoft Visual compiled script 
.pif            Shortcut to MS-DOS program 
.prf            Microsoft Outlook profile settings
.prg            Visual FoxPro Program 
.reg            Registration entries 
.scf            Windows Explorer command
.scr            Screen saver 
.sct            Windows Script Component 
.sh		Shell Script
.shb            Shell Scrap object
.shs            Shell Scrap object 
.url            Internet shortcut 
.vb             VBScript file 
.vbe            VBScript Encoded script file 
.vbs            VBScript file 
.wmf            Windows Metafile
.wmz		Windows Media File
.wsc            Windows Script Component 
.wsf            Windows Script file 
.wsh            Windows Script Host Settings file 

It is possible that other extensions will have to be blocked in the future, given that virus authors frequently use new approaches.