Microsoft is about to make it harder to send and receive certain Outlook email attachments, and if you use the New Outlook for Windows or Outlook on the web, you’ll feel the change first.
According to a report from Neowin, Microsoft has confirmed that email security is getting stricter, with more attachments being blocked across its newer Outlook clients. Here’s what we know so far — and what it means for your inbox.
How Outlook email attachments are changing
Microsoft is expanding the range of attachments it blocks in the New Outlook for Windows and the browser-based version of Outlook. The company frames the move as part of a broader push to tighten email security, though it has not yet published the full list of what will be affected.
At this point, the specifics remain thin. Microsoft has not released an exact list of file types, a rollout date, or the precise rules that will trigger a block. If you’re waiting for a detailed changelog, that document does not exist yet — the announcement is still at the “stricter is coming” stage, and the Neowin report is the primary source for these details.
Why Microsoft is tightening attachment security
Email remains one of the most common ways that malware and phishing reach people’s computers. Malicious attachments can carry ransomware, credential stealers, and other threats, which is why Microsoft and other providers have spent years building attachment scanning and blocking into their platforms.
This latest move fits into that ongoing strategy. By blocking more attachment categories before they even reach your inbox, Microsoft is trying to stop threats at the edge rather than relying solely on antivirus software to catch them after the fact. Microsoft has long offered attachment protection through services like Defender for Office 365 and its Safe Attachments feature, and broadening what gets blocked by default in the consumer-facing Outlook clients is a natural extension of that work.
New Outlook vs. Classic Outlook
It’s worth noting which Outlook you’re using, because this change targets the newer clients specifically.
The New Outlook for Windows is Microsoft’s web-based reimagining of the desktop app, built on the same underlying technology as Outlook on the web. It launched as a preview and reached general availability in 2024, and it’s the version that shows a “New Outlook” toggle in the corner of the classic app. More users are being migrated to it over time, which is likely why Microsoft chose it as the testing ground for stricter rules.
The classic Outlook for Windows — the traditional desktop client that many enterprise and power users still rely on — is not part of this change. If you’re on the legacy app, your attachment behavior should stay the same for now.
What this means for you
For most everyday users, the practical effect is simple: some attachments you previously could send or receive may get blocked. This often shows up as an error when trying to send a file, or a warning that a received attachment has been removed or quarantined before you could open it.
If you regularly share files that fall into a newly restricted category, you may need to switch to an alternative delivery method — such as a cloud link from OneDrive, SharePoint, or another file-sharing service. Microsoft has long pushed users toward cloud-based sharing for exactly this reason, so expect that pattern to continue.
How to get it and what to do
Because this is a server-side and client-level change rolling out to the New Outlook and web versions, there’s nothing to install manually. Once the change reaches your account, you’ll see it reflected automatically as you use those clients.
In the meantime, here are a few sensible steps:
- Keep an eye on Microsoft’s official communications for the full list of restricted attachment types and the rollout timeline.
- If you rely on a particular file type for work, test it now and have a cloud-sharing fallback ready.
- For enterprise admins, check with your IT team, since attachment policies can also be managed through Microsoft 365 admin controls.
Until Microsoft shares more detail, treat this as a warning sign that your attachment options in the New Outlook and web are about to narrow — and plan your file-sharing habits accordingly.
Source: Neowin
Over to you: What attachment type do you think Microsoft should block, and what would you do if a file you use every day got caught in the net?
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