Administrator Manual - Attachment Blocker

This manual contains a list of commonly blocked file formats, supported by the Retarus Email Security Attachment Blocker. Additional information about this feature is available as part of Administrator Manual - Email Security.

Commonly blocked file formats

These file formats are recommended by Retarus for the blocklist of the Attachment Blocker as they are common threat vectors for malware. This list is not exhaustive. It is up to you as an administrator which file types to block. An individual descision is necessary as blocking all these types could disrupt your workflow.

As an example, “application/x-x509-ca-cert“ is listed below as potential threat vector, but you have to decide if blocking these certificate files makes sense for your organization.

Listed below are file extensions as well as MIME types, as the Retarus Email Security Attachment Blocker is able handle both (and identify the real MIME type if the file ending had been changed). Therefore, also two separate blocklists exist and may be used.

MIME types are only listed if it might be useful to block them completely; e.g., MIME types like “text/plain” or the generic “application/octet-stream” should not be blocked.

File extension	Name / Type	MIME type
*.air	Adobe AIR Installer Package	application/vnd.adobe.air-application-installer-package+zip
*.apk	Android Package	application/vnd.android.package-archive
*.app	Executable Application
*.appx	Windows 8 App Package
*.appxbundle	Windows 8 App Package
*.asp	Active Server Page
*.bas	BASIC Source Code
*.bat	Batch Processing	application/x-msdownload
*.cab	Archive file format	application/vnd.ms-cab-compressed
*.cer	Internet Security Certificate File	application/pkix-cert
*.chm	Compiled HTML Help	application/vnd.ms-htmlhelp
*.cla	Java class file	application/vnd.claymore
*.class	Java class file	application/java-vm
*.cmd	Command File for Windows NT
*.cnt	Help file index
*.com	Command	application/x-msdownload
*.cpl	Windows Control Panel Extension
*.crt	Certificate File	application/x-x509-ca-cert
*.csh	csh Script	application/x-csh
*.der	DER Encoded X509 Certificate File	application/x-x509-ca-cert
*.diagcab	Microsoft Support diagnostic tools
*.dll	Dynamic Link Library	application/x-msdownload
*.dmg	Apple Disk Image	application/x-apple-diskimage
*.docm	Microsoft Word document including macros	application/vnd.ms-word.document.macroEnabled.12
*.dotm	Microsoft Word template including macros	application/vnd.ms-word.template.macroEnabled.12
*.emz	Tar Archive	application/x-gzip
*.exe	Executable File	application/x-msdownload
*.fxp	Visual FoxPro Compiled Source (Microsoft)
*.gadget	Windows sidebar gadget
*.grp	Windows Program Group
*.gz	Tar Archive	application/x-gzip
*.hlp	Windows Help File	application/winhlp
*.hpj	Project file used to create Windows Help File
*.hta	Hypertext Application
*.img	Disc Image Data File
*.inf	Information or Setup File
*.ins	IIS Internet Communications Settings (Microsoft)
*.iso	Disk Image	application/x-iso9660-image
*.isp	IIS Internet Service Provider Settings (Microsoft)
*.its	Internet Document Set
*.jar	Java archive file	application/java-archive
*.jnlp	Java Network Launch Protocol	application/x-java-jnlp-file
*.js	JavaScript Source Code	application/javascript
*.jse	JScript Encoded Script File
*.ksh	UNIX Shell Script
*.lib	Static library
*.lnk	Windows Shortcut File
*.lzh	Compressed Archive File	application/x-lha, application/x-compress
*.msc	Microsoft Management Console Snap-in Control File
*.msh	Microsoft Shell
*.msh1	Microsoft Shell
*.msh1xml	Microsoft Shell
*.msh2	Microsoft Shell
*.msh2xml	Microsoft Shell
*.mshxml	Microsoft Shell
*.msi	Windows Installer File	application/x-msdownload
*.msp	Windows Installer Update
*.mst	Windows SDK Setup Transform Script
*.msu	Windows Update file
*.nsh	Notes Database	application/vnd.lotus-notes
*.ocx	ActiveX Control file
*.ops	Office Profile Settings File
*.osd	Open Software Description
*.pdf	Adobe Portable Document Format	application/pdf
*.pif	Windows Program Information File (Microsoft)
*.pl	Perl script
*.plg	Developer Studio Build Log
*.potm	Microsoft PowerPoint Template including macros	application/vnd.ms-powerpoint.template.macroEnabled.12
*.ppam	Microsoft PowerPoint add-in including macros	application/vnd.ms-powerpoint.addin.macroEnabled.12
*.ppsm	Microsoft PowerPoint Slideshow including macros	application/vnd.ms-powerpoint.slideshow.macroEnabled.12
*.pptm	Microsoft PowerPoint Presentation including macros	application/vnd.ms-powerpoint.presentation.macroEnabled.12
*.prf	Windows System File / Outlook profile file	application/pics-rules
*.prg	Program File
*.printerexport	Printer backup file
*.ps1	Windows PowerShell
*.ps1xml	Windows PowerShell
*.ps2	Windows PowerShell
*.ps2xml	Windows PowerShell
*.psc1	Windows PowerShell
*.psc2	Windows PowerShell
*.psd1	Windows PowerShell
*.psdm1	Windows PowerShell
*.pst	Microsoft Exchange Address Book File, Outlook Personal Folder File	application/vnd.ms-outlook
*.rar	RAR Archive	application/x-rar-compressed
*.reg	Registration Information/Key for W95/98, Registry Data File
*.scf	Windows Explorer Command
*.scr	Windows Screen Saver
*.sct	Windows Script Component
*.shb	Windows Shortcut into a Document
*.shs	Shell Scrap Object File
*.sys	Windows System File
*.tgz	Tar Archive	application/x-gzip
*.theme	Desktop theme file settings
*.tmp	Temporary File/Folder
*.url	Internet Location	message/external-body
*.vb	VBScript File or Any VisualBasic Source
*.vbe	VBScript Encoded Script File
*.vbp	Visual Basic project file
*.vbs	VBScript Script File, Visual Basic for Applications Script	text/vbscript
*.vsmacros	Visual Studio .NET Binary-based Macro Project (Microsoft)
*.vsw	Microsoft Visio Workspace File	application/vnd.visio
*.vxd	Virtual Device Driver
*.webpnp	Internet printing file
*.website	Pinned site shortcut from Internet Explorer
*.ws	Windows Script File
*.wsc	Windows Script Component	text/scriptlet
*.wsf	Windows Script File
*.wsh	Windows Script Host Settings File
*.xbap	XAML Browser Application	application/x-ms-xbap
*.xla	Microsoft Excel add-in or macro
*.xlam	Microsoft Excel add-in including macros	application/vnd.ms-excel.addin.macroEnabled.12
*.xll	Microsoft Excel add-in
*.xlsb	Excel Binary Workbook including macros	application/vnd.ms-excel.sheet.binary.macroEnabled.12
*.xlsm	Microsoft Excel sheet including macros	application/vnd.ms-excel.sheet.macroEnabled.12
*.xltm	Microsoft Excel template	application/vnd.ms-excel.template.macroEnabled.12
*.xnk	Exchange Public Folder Shortcut
*.zip	ZIP Archive	application/zip