Here you go - the list is long - but complete - these are not acceptable files via email attachements:


adeAccess Project Extension (Microsoft)
adpAccess Project (Microsoft)
appExecutable Application
asp

Active Server Page
aspxASP.NET Web Page
asxAdvanced Stream Redirector
basBASIC Source Code
batBatch Processing
cerInternet Security Certificate File
chmCompiled HTML Help
cmdDOS CP/M Command File Command File for Windows NT
cntIndex file for Windows help files
comCommand
cplWindows Control Panel Extension (Microsoft)
crtCertificate File
cshcsh Script
derX509 Certificate
exeExecutable File
fxpFoxPro Compiled Source (Microsoft)
gadgetWindows Vista gadget
hlpWindows Help File
hpjMicrosoft Help Project File
htaHypertext Application
htcHTML Component File
infInformation or Setup File
insIIS Internet Communications Settings (Microsoft)
ispIIS Internet Service Provider Settings (Microsoft)
itsInternet Document Set Internet Translation
jsJavaScript Source Code
jseJScript Encoded Script File
kshUNIX Shell Script
libStatic DLL Library Information File
lnkWindows Shortcut File
madAccess Module Shortcut (Microsoft)
mafAccess (Microsoft)
magAccess Diagram Shortcut (Microsoft)
mamAccess Macro Shortcut (Microsoft)
maqAccess Query Shortcut (Microsoft)
marAccess Report Shortcut (Microsoft)
masAccess Stored Procedures (Microsoft)
matAccess Table Shortcut (Microsoft)
mauAccess Shortcut Function
mavAccess View Shortcut (Microsoft)
mawAccess Data Access Page (Microsoft)
mdaAccess Add-in (Microsoft) MDA Access 2 Workgroup (Microsoft)
mdbAccess Application (Microsoft) MDB Access Database (Microsoft)
mdeAccess MDE Database File (Microsoft)
mdtAccess Add-in Data (Microsoft)
mdwAccess Workgroup Information (Microsoft)
mdzAccess Wizard Template (Microsoft)
mscMicrosoft Management Console Snap-in Control File (Microsoft)
mhtWeb Page Archive File
mhtmlWeb Page Archive File
msh3D Modeling File
msiWindows Installer File (Microsoft)
mspWindows Installer Patch
mstWindows SDK Setup Transform Script
msh1Microsoft Help File
msh2Microsoft Help File
mshmxlMicrosoft Help File
msh1xmlMicrosoft Help File
msh2xmlMicrosoft Help File
opsOffice Profile Settings File
osdOpen Software Description File
pcdVisual Test (Microsoft)
pifWindows Program Information File (Microsoft)
plgAston Shell Plug-in
prfWindows System File
prgProgram File
pstMS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
regRegistration Information/Key for W95/98 Registry Data File
scfWindows Explorer Command
scrWindows Screen Saver
sctWindows Script Component Foxpro Screen (Microsoft)
shbWindows Shortcut into a Document
shsShell Scrap Object File
sysWindows System File
ps1Windows PowerShell Script
ps1xmlWindows PowerShell Script
ps2Windows PowerShell Script
ps2xmlWindows PowerShell Script
psc1Windows PowerShell Script
psc2Windows PowerShell Script
tmpTemporary File/Folder
urlInternet Location
vbVBScript File or Any VisualBasic Source
vbeVBScript Encoded Script File
vbsVBScript Script File Visual Basic for Applications Script
vpbVisual Basic Project File 
vsmacrosVisual Studio .NET Binary-based Macro Project (Microsoft)
vssVisio Stencil (Microsoft)
vstVisio Template (Microsoft)
vswVisio Workspace File (Microsoft)
vxdWindows Virtual Device Driver
wsWindows Script File
wscWindows Script Component
wsfWindows Script File
wshWindows Script Host Settings File
xnkExchange Shortcut 
xmlExtensible Mark Up Language