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MC379408: Exchange Online-Updates to the file type list in the common attachment filter

Updated July 05, 2022: We have updated the rollout timeline below and provided additional details. Thank you for your patience.

Updated June 23, 2022: We have updated the rollout timeline below. Thank you for your patience.

Updated June 1, 2022: We have updated this message to ensure visibility for affected organizations. Thank you for your patience.

In anti-malware policies, you can select specific file types to identify as malware using the common attachment filter. Any email message with attachments of these specific file types will be handled per the policy settings. You can configure this specific list of file types by selecting them from the pre-defined list in the policy properties in the Microsoft 365 Defender portal or by manually adding your own (custom) file types using the power shell Set-MalwareFilterPolicy cmdlet in Exchange Online PowerShell.

We are enhancing the common attachments filter (Anti-malware policy) to expand list of available file types and also manage custom file types in the portal.

MC379408: Exchange Online-Updates to the file type list in the common attachment filter

Based on internal research and best practices guidelines from industry and other organizations, we are updating the list of file types that are available for selection. Currently, there are 95+ file types in the list, of which 13 are pre-selected by default in the common attachment filter settings. We are expanding this list to cover over 200 file types, of which over 50 are selected by default.

After rollout, this new expanded list along with the default selection will automatically apply to:

  1. Any new anti-malware policies that you create
  2. The default anti-malware policy: The current list of the selection will be retained and appended with the new file types being added as part of default selection. As a result, the list of file selections in the default policy will be expanded while retaining all of the existing selection. There will be no changes to any of the other settings (like zap, admin notification configuration etc). The only change which will happen to the default policy is the expansion of the selection.

The file selections in your existing anti-malware policies (enabled or not) will be retained and will not be updated automatically. You will need to manually update your existing policies with the recommended list of default file types (see below).

This message is associated with Microsoft 365 Roadmap ID 85611.

When this will happen

Starting mid-July (previously early July) and completion of deployment by mid-August (previously late July)

How this will affect your organization

Once these changes are rolled out, the list of default file type selections to the newly created policies and the default policy will differ from your existing policies. As the selection in the default policy will be expanded, there could be some messages which could be quarantined due to new file type addition. You will need to review the existing policies and update the list with recommended file types (see below).

What you need to do to prepare

Review existing anti-malware policies and add the recommended file types to the block list. Since the default policy will now cover more file types, it’s likely that the expanded list of files in the default policy will block messages. If you do not want the new list of file types to be active, create a custom anti-malware policy (soon, before this feature deployment) with the file types that meet your needs.

Learn more

Review the following resources below to learn more:

The list of file types:

7z, 7zip,

a, accdb, accde,ace, action, ade, adp, apk, app, appx, appxbundle, arj, asf, asp, aspx, ani, avi,

bat, bin, bundle, bz, bz2, bzip2,

cab, caction, cer, chm, cmd, com, command, cpl, crt, csh, css,

deb, der, dex, dgz, dll, dmg, doc, docm, docx, dot, dotm, dtox, dylib,

elf, exe,

font,

gz, gzip,

hlp, hta, htm, html,

img, imp, inf, ins, ipa, iso, isp, its,

jar, jnlp, js, jse,

kext, ksh,

lha, lib, library, lnk, lqy, lzh,

macho, mad, maf, mag, mam, maq, mar, mas, mat, mav, maw, mda, mdb, mde, mdt, mdw, mdz, mht,

mhtml, msc, mscompress, msh, msh1, msh1xml, msh2, msh2xml, mshxml, msi, msix, msixbundle, msp, mst,

o, obj, odp, ods, odt, one, onenote, ops,

package, pages, pbix, pdb, pdf, php, pif, pkg, plugin, ppa, ppam, pps, ppsm, ppsx, ppt, pptm, pptx, prf,

prg, ps1, ps1xml, ps2, ps2xml, psc1, psc2, pst, pub, py,

rar, reg, rev, rpm, rtf,

scf, scpt, scr, sct, service, sh, shx, shb, shtm, so, sys,

tar, tarz, terminal, tgz, tool,

uif, url,

vb, vbe, vbs, vhd, vsd, vsdm, vsdx, vsmacros, vss, vssx, vst, vstm, vstx, vsw, vxd,

workflow, ws, wsc, wsf, wsh,

xhtml, xla, xlam, xll, xls, xlsb, xlsm, xlsx, xlt, xltm, xltx, xz,

z, zi, zip, zipx,

The default selection from the above file type list is:

ace, apk, app, appx, ani, arj,

bat,

cab, cmd,com,

deb, dex, dll, docm,

elf, exe,

hta,

img, iso,

jar, jnlp,

kext,

lha, lib, library, lnk, lzh

macho, msc, msi, msix, msp, mst

pif, ppa, ppam,

reg, rev,

scf, scr, sct, sys,

uif,

vb, vbe, vbs, vxd

wsc, wsf, wsh

xll, xz

z

Message ID: MC379408
Published: 13 May 2022
Updated: 05 July 2022

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

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