Which file types to block

Our email scanning is run by an external company. It has been working up to a point, but due to the large amount of spam getting through they are upgrading this service. As part of this upgrade, I have been given a list of attachment file types and asked which I want them to block and which to allow.

Half of these I am pretty sure about, but I need some guidance on what some of the others are and whether they are a genuine security threat.

Here's what I have left...

Binary - encrypted

Binary - not protected

LZH compressed archive (if we allow .zip, any reason not to allow these?)

Binhex

Microsoft Compress

TNEF

Possible install shield

PEM - Privacy enhanced mail (we are allowing PGP, so why not these?)

ARJ (see LZH comment)

TAR

CMP

GZP

UUE

Apple double resource fork

Apple single

CDA

DCX

Embedded OLE Object

Embedded OLE Package

JTD

Lotus 123

MS Project - MPP

Pattern matched

XML

Win32 Unknown Executable

DWG

PPM

WMF

PCX

PKCS message



Then, is there any reason to allow any of these scripts in a business email message...

Javascript, JavascriptEncoded, Unknown Script, VBScript, VBScriptEncoded


Thanks

 

Best rule of thumb to follow is, block ALL. Only allow what you KNOW that you need. It's better to have your security TOO tight, and have to ease up on it, then have it too open, and find out the hard way that you need to start blocking something.

Scott
http://www.AAApcMechanic.com