How to Attach Mail in Outlook: A Complete Guide to Email Attachments

Attaching files, emails, or other items in Microsoft Outlook is one of the most common tasks in any professional workflow — but the process varies more than most people expect. Whether you're attaching a document, a photo, a calendar item, or even another email, Outlook gives you several methods to do it. Understanding which method applies to your situation makes the difference between a smooth send and a frustrating workaround.

What "Attaching Mail" Can Mean in Outlook

The phrase "attach mail in Outlook" actually covers two distinct actions:

1. Attaching a file (document, image, PDF, etc.) to an email you're composing
2. Attaching another email as an item within a new message

Both are valid and common, but they work differently. Knowing which one you need is the first step.

How to Attach a File to an Email in Outlook 📎

This is the most straightforward type of attachment. Here's how it works across the main Outlook interfaces:

In Outlook Desktop (Windows or Mac)

1. Open a new email by clicking New Email or reply to an existing message
2. In the message window, go to the Insert tab in the ribbon
3. Click Attach File
4. Choose from recently used files, browse your computer, or link from OneDrive or SharePoint
5. Select your file and click Insert

Alternatively, you can drag and drop a file directly from File Explorer (Windows) or Finder (Mac) into the message body.

In Outlook on the Web (OWA)

1. Start a new email or reply
2. Click the paperclip icon at the bottom of the compose window
3. Choose Attach as a copy (uploads the file) or Share as a OneDrive link (for larger files or collaborative purposes)
4. Browse and select your file

In the Outlook Mobile App (iOS or Android)

1. Compose a new message or reply
2. Tap the paperclip icon or the attachment icon in the toolbar
3. Choose from your files, photos, or cloud storage
4. Tap to attach

How to Attach One Email to Another Email in Outlook

This is where Outlook has a distinct advantage over many email clients. You can forward an email as an attachment rather than inline text — useful when you want to preserve the original formatting, headers, and metadata.

Method 1: Drag and Drop (Desktop Only)

1. Open a new message window
2. In your inbox or folder list, find the email you want to attach
3. Click and drag that email into the body of your new message
4. It will appear as an .msg file attachment, not inline text

This is the fastest method for Outlook desktop users and preserves the full original email as a file the recipient can open directly.

Method 2: Forward as Attachment (Desktop)

1. Select the email you want to attach
2. Go to Home tab → Respond group → click the More (…) or Forward dropdown
3. Choose Forward as Attachment
4. A new compose window opens with the original email already attached as a .msg file
5. Add your recipient and any message text, then send

Method 3: Using the Insert Item Feature

1. While composing a new email, go to the Insert tab
2. Click Outlook Item
3. Browse your folders and select the email you want to attach
4. Choose to insert it as Text only or as an Attachment
5. Click OK

This method works well when you need to search across multiple folders to find a specific message.

Key Variables That Affect How Attachments Work

Not all Outlook setups behave identically. Several factors shape your experience:

File size is one of the most common pain points. If your attachment exceeds your server's limit, Outlook may automatically offer to upload it to OneDrive and share a link instead — or it may simply bounce the message.

Attaching Files vs. Sharing Links: An Important Distinction

Modern Outlook (especially with Microsoft 365) increasingly nudges users toward sharing cloud links rather than attaching full file copies. Here's what each approach means in practice:

• Attaching a copy: The file is embedded in the email. Recipients get their own copy. No internet connection required to open it after download. File size counts against limits.
• Sharing a OneDrive or SharePoint link: The file stays in the cloud. Recipients click the link to view or edit. Ideal for large files or collaborative documents. Requires the recipient to have access permissions.

Which approach is better depends on your workflow, the recipient's setup, whether collaboration is needed, and your organization's file-sharing policies.

Common Attachment Issues and What Causes Them

• "File is too large" — Exceeds the server's size limit; try compressing the file or using a cloud link
• "File type not permitted" — Certain extensions are blocked by default for security reasons; your IT admin controls this
• Attachment not showing — Sometimes occurs in plain text mode; switching to HTML format usually resolves it 🔍
• Drag-and-drop not working — Often a permissions or window-focus issue on Windows; try the Insert tab method instead

How Your Setup Shapes the Right Approach

A solo user on a personal Microsoft account, a corporate employee on an Exchange server, and a small business owner using Outlook with a third-party email host will all have meaningfully different experiences with attachments. File size caps, blocked file types, cloud integration depth, and available features all depend on which version of Outlook you're running, how your account is configured, and what policies (if any) govern your environment.

Understanding those layers — your Outlook version, your account type, and any organizational restrictions — is what determines which attachment method will actually work for you.