The basic way to attach a file in Outlook

To attach a file in Outlook, open a new email or reply to one you've received. Look for the Attach button — it's usually a paperclip icon in the toolbar at the top of the compose window. Click it, then browse your computer to find the file you want to send. Select the file and click Open. The file name will appear in the attachment area below the subject line.

That's the standard method, and it works the same way whether you're using Outlook on Windows, Mac, or the web version. Once you've attached the file, you can add more files by clicking the paperclip again, or you can drag files directly into the compose window if your version of Outlook supports it.

Before you send, check that the attachment actually appears in the compose window. A common mistake is clicking attach, selecting a file, but then not confirming the selection — the file browser closes but nothing gets added to your email. If you don't see the file name listed, try again.

Key Takeaways

  • Click the paperclip icon in the compose toolbar, browse to your file, and click Open to attach it to your email.
  • You can attach multiple files by clicking the paperclip again for each one, or by dragging files directly into the compose window.
  • Always verify that the file name appears in the attachment area before you send, because the file browser closing does not mean the file was attached.
  • File size limits vary by email provider — Outlook.com allows up to 20 MB per file, while some workplace servers may have smaller limits.
  • If an attachment fails to send, try compressing the file or using cloud storage to share it instead.

Where to find the Attach button in different versions of Outlook

In Outlook on Windows (desktop), the paperclip icon sits in the toolbar at the top of the compose window, usually near the formatting buttons. If you don't see it when ready, look for a row of icons that includes Bold, Italic, and Underline — the paperclip is typically nearby.

In Outlook on Mac, the paperclip is in the same location at the top of the compose window. In Outlook on the web (the version you access through a browser), click the paperclip icon, which appears in the toolbar above the message body. If you're using an older version of Outlook, the button may be labeled Insert instead of showing just a paperclip icon — click that and look for an Attach File option.

If you cannot find the attach button at all, try right-clicking in the compose window. Some versions of Outlook show an Attach File option in the context menu. You can also use the keyboard shortcut Ctrl+Shift+A (Windows) or Command+Shift+A (Mac) to open the file browser directly.

File size limits and what happens when you exceed them

Outlook.com allows attachments up to 20 MB per file. If you try to attach something larger, Outlook will warn you before you send. Other email providers have different limits — Gmail allows 25 MB, while some workplace email servers allow only 10 MB or less. Your IT department can tell you what your organization's limit is.

If your file is too large, Outlook may offer to upload it to OneDrive (Microsoft's cloud storage) and send a link instead. This is usually the easiest solution. You can also compress the file yourself using Windows' built-in compression tool (right-click the file, select Send To, then Compressed Folder) or a tool like 7-Zip, which often reduces file size significantly.

If compression doesn't help enough, consider uploading the file to OneDrive, Google Drive, or Dropbox and sending a link instead. This also protects you if the recipient's email server rejects large attachments — a link works around that problem entirely.

Attaching files from cloud storage instead of your computer

You don't have to attach files from your hard drive. In Outlook on the web and in recent versions of the desktop app, you can attach files directly from OneDrive, SharePoint, or Google Drive. Click the Attach button and look for an option like Browse Cloud Locations or OneDrive. Select the file from your cloud storage, and Outlook will insert a link to it rather than copying the whole file into the email.

This method has real advantages: the file doesn't count against your attachment size limit, the recipient always sees the most current version if you update it later, and you can control who can view it by adjusting the sharing settings in your cloud storage. It also means the recipient doesn't end up with multiple copies of the same file in their inbox.

The trade-off is that the recipient needs access to your cloud storage account to open the file. If you're sending to someone outside your organization or someone who doesn't have a Microsoft account, attaching the file directly is usually simpler.

Why an attachment might fail to send

The most common reason an attachment fails to send is that the file is too large for your email provider's limit. You'll usually get an error message saying so. The second most common reason is that your email server is blocking the file type for security reasons — executable files (.exe), script files (.bat, .cmd), and some other types are often blocked automatically.

If your attachment is blocked, you have a few options. You can compress it into a .zip file, which sometimes bypasses the block. You can upload it to cloud storage and send a link instead. Or, if you're sending to someone in your organization, ask your IT department whether they can whitelist the file type.

Less commonly, an attachment fails because the file is corrupted or because your internet connection dropped during the send. If this happens, try attaching the file again, or try a different file to see whether the problem is with that specific file or with your email connection.

How to spot a suspicious attachment before you open it

An attachment is suspicious if the sender is someone you don't recognize, if the email asks you to enable macros or click a link to "verify" something, or if the file type seems wrong for what the sender claims to be sending. For example, if someone says they're sending you a photo but the attachment is a .exe or .zip file, that's a red flag.

Hover over the attachment name to see the full file name and extension. Scammers sometimes hide the real extension by naming a file something like "Invoice.pdf.exe" — it looks like a PDF but it's actually an executable program. If you're unsure whether an attachment is safe, ask the sender to confirm they sent it, or scan it with antivirus software before opening it.

Microsoft Outlook has built-in protections that block certain file types automatically. If you receive an attachment that Outlook won't let you open, that's usually a sign it's potentially dangerous. Don't try to work around the block — ask the sender to resend it in a safer format.

Frequently Asked Questions

Can I attach a folder instead of individual files?

No, email doesn't support attaching folders directly. You have to attach individual files. If you need to send multiple files, either attach them one at a time, or compress the folder into a single .zip file and attach that. The recipient can then unzip it on their end to get all the files back.

What if the recipient says they didn't receive my attachment?

First, check that the file name actually appears in the attachment area of your sent email — open the email from your Sent folder and verify it's there. If it is, the attachment was sent but the recipient's email server may have blocked it, or they may have accidentally deleted it. Ask them to check their spam or junk folder. If it's not in your sent email, the attachment didn't send and you need to try again.

Is it safe to open attachments from people I don't know?

No. Don't open attachments from unknown senders, especially if the email is asking you to do something urgent or unusual. Scammers use attachments to deliver malware. If you're not expecting an attachment from someone, ask them to confirm they sent it before you open it.

Can I attach a password-protected file?

Yes, you can attach any file type that Outlook allows, including password-protected documents. However, the recipient will need the password to open it, so you'll have to send the password separately — never in the same email as the attachment.

What's the difference between attaching a file and inserting it as a link?

Attaching a file copies it into the email, so the recipient gets their own copy. Inserting a link (from OneDrive or another cloud service) sends only a link, and the recipient opens the file from your cloud storage. Links are better for large files and when you want the recipient to always see the latest version. Attachments are better when you want the recipient to have their own copy or when they don't have access to your cloud storage.