One of the most common ways of transmitting computer viruses is through file attachments. Outlook blocks the sending and receiving of certain types of files (such as .exe and certain database files) as attachments to help protect you and your recipients against computer viruses. We recommend using OneDrive and sending the recipient a link to the file if you need to send one of these file types to an email recipient.

Note: If you're using a Microsoft Exchange account, your email server administrator can unblock certain file types. Contact your administrator for more assistance.

Share files through the cloud

If you need to send a file that's blocked by Outlook, the simplest way to send your file is to upload it to OneDrive or a secure network share server such as SharePoint. Then send a link to the file. If you need to receive a blocked file, ask the sender to upload the file to OneDrive or SharePoint and send you a link. Once you receive the link, you can open the file location and download the file.
 
Note: For OneDrive and OneDrive for Business, you'll need to ask the sender to only send you a link to the file rather than attach the file to the email using OneDrive. To obtain a sharing link in OneDrive, highlight the file and choose Get Link in the menu bar.

File types blocked in Outlook

File name extension

File type

.ade

Access Project Extension (Microsoft)

.adp

Access Project (Microsoft)

.app

Executable Application

.appcontent-ms

Microsoft Windows Application Content

.application

ClickOnce Deployment Manifest File

.appref-ms

ClickOnce Application Reference File

.asp

Active Server Page

.aspx

Active Server Page Extended

.asx

ASF Redirector File

.bas

BASIC Source Code

.bat

Batch Processing

.bgi

Borland Graphics Interface

.cab

Windows Cabinet File

.cdxml

ChemDraw XML

.cer

Internet Security Certificate File

.chm

Compiled HTML Help

.cmd

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

.cnt

Microsoft Help Workshop Application

.com

Command

.cpl

Windows Control Panel Extension (Microsoft)

.crt

Certificate File

.csh

csh Script

.der

DER Encoded X509 Certificate File

.diagcab

Microsoft Diagnostics Cabinet File

.exe

Executable File

.fxp

FoxPro Compiled Source (Microsoft)

.gadget

Windows Vista Gadget

.grp

Microsoft Program Group

.hlp

Windows Help File

.hpj

AppWizard Help project

.hta

Hypertext Application

.htc

HTML Component File

.img

Image

.inf

Information or Setup File

.ins

IIS Internet Communications Settings (Microsoft)

.iso

Optical Disk Media File System

.isp

IIS Internet Service Provider Settings (Microsoft)

.its

Internet Document Set, Internet Translation

.jar

Java Archive

.jnlp

Java Network Launching Protocol

.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)

.mcf

Media Container Format

.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)

.mht

Web HTML

.mhtml

Web HTML

.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

.msu

Windows Update File

.ops

Office Profile Settings File

.osd

Open Software Description 

.pcd

Visual Test (Microsoft)

.pif

Windows Program Information File (Microsoft)

.pl

Perl script

.plg

Developer Studio Build Log

.prf

Windows System File

.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

.pssc

Windows PowerShell Session Configuration

.pst

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

.py

Python Script

.pyc

Python Script

.pyo

Python Script

.pyw

Python Script

.pyz

Python Script

.pyzw

Python Script

.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)

.settingcontent-ms

Windows Shortcut file

.shb

Windows Shortcut into a Document

.shs

Shell Scrap Object File

.theme

Desktop Theme File Settings

.tmp

Temporary File/Folder

.url

Internet Location

.vb

VBScript File or Any Visual Basic Source

.vbe

VBScript Encoded Script File

.vbp

Visual Basic Project File

.vbs

VBScript Script File, Visual Basic for Applications Script

.vhd

Virtual Hard Disk

.vhdx

Virtual Hard Disk Extended

.vsmacros

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

.vsw

Visio Workspace File (Microsoft)

.webpnp

Internet Printing File

.website

Pinned Site Shortcut from Internet Explorer

.ws

Windows Script File

.wsb

Windows Sandbox file

.wsc

Windows Script Component

.wsf

Windows Script File

.wsh

Windows Script Host Settings File

.xbap

Browser Applications

.xll

Excel Addin

.xnk

Exchange Public Folder Shortcut

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