Attaching a document in Outlook takes three steps: click the paperclip icon, select your file, and send

When you are composing an email in Outlook, the attachment button sits in the toolbar at the top of your message. Click the paperclip icon, browse to the file you want to send, select it, and it appears in your email. The file stays attached until you send the message or delete it. Outlook works the same way whether you use the desktop app on Windows or Mac, the web version at outlook.com, or Outlook on your phone.

The most common mistake is attaching the wrong file or forgetting to attach anything after you mention it in the message. Before you hit send, look at the attachment area to confirm the right file is there and the file size is reasonable for email.

Key Takeaways

  • The paperclip icon in the compose toolbar opens your file browser so you can select what to attach.
  • You can attach multiple files at once by holding Ctrl (Windows) or Command (Mac) while clicking each file name.
  • Outlook shows you the file size before you send, so you can check whether it is too large for your recipient's email system.
  • If you mention an attachment in your message but forget to add one, Outlook can warn you before you send.

Attaching a single file on desktop Outlook

Open Outlook and start a new email by clicking "New Email" or pressing Ctrl+N. Type your recipient's address, subject line, and message. When you are ready to add a file, look at the toolbar above the message body and click the paperclip icon. This opens your file browser.

Navigate to the folder where your file lives. Click the file once to select it, then click "Insert" or "Open" at the bottom right of the window. The file name now appears in the attachment area below the subject line. You can see the file size next to the name. If you need to remove it, click the X next to the file name.

Attaching multiple files at once

You can attach more than one file in a single step. After you click the paperclip icon and the file browser opens, hold down Ctrl (on Windows) or Command (on Mac) and click each file you want to attach. All the files you select will highlight. Click "Insert" or "Open" and all of them attach to your email at once.

If you prefer to add files one at a time, that works too — just click the paperclip icon again and repeat the process. There is no limit to how many files you can attach, but keep in mind that very large attachments can bounce back if your recipient's email system has size restrictions.

Attaching files in Outlook on the web

If you use Outlook at outlook.com in your browser, the process is slightly different. Click "New Message" to start composing. Type your recipient, subject, and message. Then look for the paperclip icon in the toolbar — it is usually near the formatting buttons. Click it to open the file browser.

Select your file and click "Open". The file appears in the attachment area. On the web version, you can also drag and drop a file directly from your computer into the message if your browser supports it — just drag the file from your desktop or file explorer and drop it into the compose area.

Attaching files on Outlook mobile

On an iPhone or Android phone, open Outlook and tap the pencil icon to start a new message. Type your recipient and message. Then tap the paperclip icon at the bottom of the screen. On iPhone, you will see options to choose a photo, take a photo, or browse files. On Android, you usually see "Attach" or a similar option.

Tap "Browse Files" or "Files" to open your phone's file manager. Navigate to the file you want and tap it. The file attaches to your message. You can add multiple files by tapping the paperclip icon again. When you are done, tap "Send".

What to do if your file is too large

Outlook shows you the file size when you attach it. If the total size of all your attachments is more than 20 to 25 MB, some email systems may reject the message. If you see a warning or if you know the file is large, you have a few options.

You can compress the file to make it smaller — right-click the file in Windows and select "Send to" then "Compressed (zipped) folder", or on Mac, right-click and select "Compress". You can also ask your recipient if they have a file-sharing service like OneDrive or Google Drive where you can upload the file and send them a link instead. This works better for very large files like videos or high-resolution images.

Enabling attachment reminders in Outlook

Outlook can remind you if you mention an attachment in your message but forget to actually attach a file. This feature is turned on by default in most versions, but you can check your settings to make sure.

On desktop Outlook, go to "File" then "Options" then "Mail". Look for a section called "Compose messages" or "Composing". Check the box next to "Warn me when I close a message without attaching a file if I mention attachments in the message". On Outlook on the web, this feature is usually on automatically and you cannot turn it off. If you try to send a message that says "attach" or "attached" but has no files, Outlook will ask you to confirm before sending.

Frequently Asked Questions

Can I attach a file that is stored in OneDrive or SharePoint?

Yes. When you click the paperclip icon, you can browse to OneDrive or SharePoint files just like local files. Outlook treats them the same way. If the file is very large, you can also choose to send a link to the file instead of attaching the whole thing — look for an option like "Attach from cloud" or "Share a link" in the attachment menu.

What happens if I attach a file and then edit it before sending?

Outlook attaches a copy of the file at the moment you select it. If you edit the original file after attaching it, the changes do not automatically appear in the attachment. You need to delete the old attachment and add the updated file again before you send the message.

Why does Outlook say my attachment is blocked?

Some file types like .exe, .bat, or .zip files can be blocked by Outlook or your organization's email system for security reasons. If this happens, compress the file, rename the extension, or ask your recipient if they can receive it through a file-sharing service instead.

Can I attach a file from my email signature?

No. Your email signature is text only. If you want to include a file with every email you send, you need to attach it manually each time, or set up a rule in Outlook to attach a specific file automatically — this requires going into your mail rules settings, which varies by version.

What is the difference between attaching and inserting a file?

Attaching a file sends it as a separate item your recipient can download. Inserting a file embeds it into the message body itself. Use attach for documents you want the recipient to open separately. Use insert only for small images or text you want to appear directly in the email.