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Email Size Limit

The maximum size for an email message (including all attachments) is 25MB. This limit includes:
  • The email body (HTML and plain text)
  • All attachments (base64 encoded)
  • Headers and metadata
Emails exceeding 25MB will be rejected with an error. Consider using external file hosting services for large files and including download links in your email instead.

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Blocked Attachments

For security reasons, certain file types are blocked from being sent as attachments. These restrictions help protect recipients from potentially malicious files.

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Blocked File Types

The following table lists all blocked file extensions and their associated MIME types, organized by category:

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Executable Files & Applications

ExtensionMIME Type(s)Description
.exeapplication/x-msdownload, application/x-executable, application/octet-stream-exeWindows executable
.comapplication/x-msdownload, application/x-msdos-programDOS command file
.appapplication/x-ms-applicationApplication file
.msiapplication/x-msi, application/x-ms-installerWindows installer package
.mspapplication/x-msiWindows installer patch
.mstapplication/x-msiWindows installer transform
.gadgetapplication/gadget, application/x-gadgetWindows gadget
.dllapplication/x-msdownloadDynamic link library
.jarapplication/java-archiveJava archive

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Script Files

ExtensionMIME Type(s)Description
.batapplication/x-bat, application/x-cmdBatch file
.cmdapplication/x-cmd, application/x-batCommand script
.ps1application/x-powershell, text/x-powershellPowerShell script
.ps1xmlapplication/x-powershellPowerShell XML
.ps2application/x-powershell, text/x-powershellPowerShell v2 script
.ps2xmlapplication/x-powershellPowerShell v2 XML
.psc1application/x-powershellPowerShell console file
.psc2application/x-powershellPowerShell v2 console file
.vbapplication/x-vb, text/vbscriptVisual Basic file
.vbsapplication/x-vbs, text/vbscriptVBScript file
.vbeapplication/x-vbe, text/vbscriptEncoded VBScript
.jsapplication/javascript, application/x-javascript, text/javascript, text/x-scriptJavaScript file
.jseapplication/x-javascript, text/jscriptEncoded JavaScript
.wstext/x-scriptWindows script
.wsftext/x-scriptWindows script file
.wsctext/x-scriptWindows script component
.wshtext/x-scriptWindows script host
.shapplication/x-shellscript, application/x-shShell script
.cshapplication/x-cshC shell script
.kshapplication/x-shellscriptKorn shell script
.aspapplication/x-asp, application/asp, text/asp, text/x-aspActive Server Page

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System & Configuration Files

ExtensionMIME Type(s)Description
.sysapplication/x-sys, application/octet-stream-sysSystem file
.cplapplication/x-msdownloadControl panel item
.scrapplication/x-msdownloadScreen saver
.regapplication/x-regRegistry file
.inftext/plainSetup information file
.crtapplication/x-crtCertificate file
.cerapplication/x-crtSecurity certificate
.derapplication/x-crtDER certificate

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Microsoft Office & Access

ExtensionMIME Type(s)Description
.mdbapplication/x-msaccess, application/vnd.ms-accessAccess database
.mdeapplication/x-msaccessAccess compiled database
.mdaapplication/x-msaccessAccess add-in
.mdtapplication/x-msaccessAccess data file
.mdwapplication/x-msaccessAccess workgroup
.mdzapplication/x-msaccessAccess wizard
.accdbapplication/x-msaccessAccess 2007+ database
.adeapplication/x-msaccessAccess project extension
.adpapplication/x-msaccessAccess project
.madapplication/x-msaccessAccess module
.mafapplication/x-msaccessAccess file
.magapplication/x-msaccessAccess diagram
.mamapplication/x-msaccessAccess macro
.maqapplication/x-msaccessAccess query
.marapplication/x-msaccessAccess report
.masapplication/x-msaccessAccess stored procedure
.matapplication/x-msaccessAccess table
.mauapplication/x-msaccessAccess user
.mavapplication/x-msaccessAccess view
.mawapplication/x-msaccessAccess web
.pubapplication/x-mspublisherPublisher document
.vsmacrosapplication/vnd.ms-vsmacrosVisual Studio macros

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Web & Browser Files

ExtensionMIME Type(s)Description
.htaapplication/htaHTML application
.htm(when containing scripts)HTML file
.html(when containing scripts)HTML file
.urltext/x-urlInternet shortcut
.mhtmlVariousWeb archive

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Help & Documentation

ExtensionMIME Type(s)Description
.chmapplication/vnd.ms-htmlhelp, application/x-chmCompiled HTML help
.hlpapplication/winhlpWindows help file
.itsRelated to help filesInternet document set

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Shell & Shortcuts

ExtensionMIME Type(s)Description
.lnkapplication/x-ms-shortcutWindows shortcut
.pifapplication/x-pifProgram information file
.shbShell fileShell scrap object
.shsShell fileShell scrap object
.scfapplication/x-explorer-commandWindows Explorer command
.scttext/scriptletWindows script component
.xnkExchange shortcutExchange shortcut

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Installer & Package Files

ExtensionMIME Type(s)Description
.insapplication/x-internet-signupInternet settings
.ispapplication/x-internet-signupInternet service provider
.libapplication/x-archiveLibrary file
.mscapplication/x-mscManagement console
.opsOffice profileOffice profile settings
.pcdPhoto CDPhoto CD image
.prgProgram fileProgram file
.fxpFoxProFoxPro compiled

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Visual Studio & Development

ExtensionMIME Type(s)Description
.vssapplication/vnd.visioVisio stencil
.vstapplication/vnd.visioVisio template
.vswapplication/vnd.visioVisio workspace
.vxdVirtual deviceVirtual device driver

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Media Files

ExtensionMIME Type(s)Description
.wmzapplication/x-ms-wmzWindows Media skin
.emfapplication/x-msmetafileEnhanced metafile

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FoxPro Files

ExtensionMIME Type(s)Description
.basBASIC sourceBASIC source code
.prfSettings fileProfile settings
.plgPlugin filePlugin file
.mshScript shellMicrosoft Shell
.msh1Script shellMicrosoft Shell v1
.msh2Script shellMicrosoft Shell v2
.mshxmlScript shell XMLMicrosoft Shell XML
.msh1xmlScript shell v1 XMLMicrosoft Shell v1 XML
.msh2xmlScript shell v2 XMLMicrosoft Shell v2 XML

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Temporary Files

ExtensionMIME Type(s)Description
.tmpVariousTemporary file

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Miscellaneous

ExtensionMIME Type(s)Description
.applicationapplication/x-ms-applicationClickOnce deployment
.obdOffice binderOffice binder document
.mvbMultimedia viewerMultimedia viewer file
.vpsVirtual private serverVPS file

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Additional MIME Type Restrictions

The following MIME types are also blocked:
  • application/octet-stream (for executable files)
  • application/x-msdownload
  • application/x-ms-installer
  • application/x-msdos-program
  • application/x-msscript
  • application/x-ms-shortcut
  • application/x-ms-wmz
  • application/x-msmetafile
  • application/x-msbinder
  • application/x-msmediaview
  • text/scriptlet

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Why These Restrictions?

These file types are blocked because they can:
  • Execute code automatically when opened
  • Exploit vulnerabilities in email clients or operating systems
  • Bypass security measures through social engineering
  • Contain macros or scripts that could harm the recipient’s system
  • Be used to spread malware or ransomware
Most business documents (PDF, DOCX, XLSX), images (JPG, PNG, GIF), and common file formats are allowed. The restrictions focus on executable and script files that pose security risks.