Attaching an email to another email allows you to share an entire conversation, including its original formatting, headers, and metadata, without the clutter of a standard forward. When you attach an email, it typically becomes an .eml file—a universal email format—which the recipient can open to view the message exactly as it appeared in your inbox. This method is the professional standard for technical support, legal documentation, and organizational record-keeping.

Most desktop email clients like Gmail and Outlook support this via drag-and-drop or specific menu options. However, the process varies significantly between web browsers, desktop applications, and mobile devices.

Direct Methods for Attaching Emails in Gmail

Gmail provides two primary ways to attach emails to a new message on a desktop computer. These methods ensure that the original message remains intact and is treated as a distinct file attachment rather than inline text.

Using the Forward as Attachment Feature

The most straightforward way to send multiple emails as attachments in Gmail is through the inbox toolbar. This method is highly efficient when you need to bundle several related messages into a single report.

  1. Open Gmail in your web browser.
  2. Navigate to your inbox or the specific folder containing the emails you wish to share.
  3. Select the emails by clicking the checkbox to the left of each message.
  4. Once selected, look at the toolbar at the top of the message list.
  5. Click the "More" icon, represented by three vertical dots.
  6. Select "Forward as attachment" from the dropdown menu.
  7. A new "Compose" window will automatically open with the selected emails already attached as .eml files.
  8. Enter the recipient’s address, a subject line, and your message, then click "Send."

This method is preferred because it automatically handles the file conversion and creates a clean draft for you to work with immediately.

The Drag and Drop Method in Gmail

For those who prefer a more interactive workflow, Gmail supports dragging and dropping emails directly into a new draft. However, there is a specific technical requirement: the "Compose" window must be popped out or active for the drop zone to register.

  1. Click the "Compose" button to start a new email.
  2. If the compose window is in the bottom-right corner, you can drag emails into it directly from the list.
  3. If you are replying to an existing thread and want to attach a different email to that reply, click the "Type of response" button (usually a small arrow next to the recipient's name) and select "Pop out reply." This opens the reply in a separate window.
  4. Locate the email you want to attach in your message list.
  5. Click and hold the email, then drag it into the body of your new message or the reply window.
  6. You will see an "Empty" area change to "Drop files here." Release the mouse button.
  7. The email will appear at the bottom of your message as an .eml attachment.

In our testing, the drag-and-drop method is significantly faster when you are already in the middle of writing a complex response and realize you need to include a reference email from a different thread.

How to Attach Emails in Microsoft Outlook

Microsoft Outlook offers a high degree of flexibility for attaching emails, though the steps differ between the classic desktop application, the "New Outlook," and Outlook on the web.

Attaching Items in the Outlook Desktop App

In the professional versions of Outlook (Office 365 or standalone desktop apps), emails are treated as "Outlook Items." When you attach them, they are often saved as .msg files, which are native to the Windows environment but can also be converted to .eml for broader compatibility.

  1. Open the Outlook desktop application.
  2. Click "New Email" to start a fresh draft.
  3. In the ribbon at the top of the message window, click the "Insert" tab.
  4. Click the "Attach Item" button, then select "Outlook Item."
  5. A window will appear showing your entire folder hierarchy (Inbox, Sent Items, etc.).
  6. Browse to the folder and select the specific email(s) you want to include.
  7. Under the "Insert as" section on the right, ensure "Attachment" is selected (rather than "Text only").
  8. Click "OK."

The emails will now appear in the attachment line of your draft. One advantage of the desktop app is the ability to search through your folders within this selection window, which is a major time-saver for users with thousands of archived messages.

Using Drag and Drop in Outlook Web (Outlook.com)

The web version of Outlook, often used by businesses via Microsoft 365, has optimized its drag-and-drop interface to be highly intuitive.

  1. Log in to your Outlook account via a browser.
  2. Click "New Message" to open the compose pane on the right side.
  3. Locate the email you want to attach in your inbox list.
  4. Click and hold the email from the list.
  5. Drag it directly into the body of the new message you are composing.
  6. The interface will highlight a box that says "Drop messages here."
  7. Drop the email, and it will instantly convert into an .eml attachment.

Unlike Gmail, Outlook Web does not always require you to "pop out" the window, as the side-pane architecture allows for seamless dragging across the interface.

Attaching Emails in Apple Mail and Other Platforms

Apple Mail users on macOS have a distinct built-in feature that simplifies this process, making it arguably the most user-friendly for desktop power users.

Apple Mail for macOS

  1. Open Apple Mail.
  2. Select the email or multiple emails you want to forward.
  3. Go to the top menu bar and select "Message."
  4. Click "Forward as Attachment."
  5. Alternatively, you can simply drag an email from the message list and drop it into any open "New Message" window.

Apple Mail is particularly good at preserving the original structure of the email, and the resulting .eml files are highly compatible with both Windows and mobile recipients.

Yahoo Mail and Proton Mail

Platforms like Yahoo do not always have a "Forward as Attachment" button. In these cases, the "Download" workaround is necessary:

  • Yahoo: Open the email, click the "More" (three dots) menu, and select "Download Message." This saves the email as an .eml file to your computer. Then, compose a new email and attach that file as you would a photo or document.
  • Proton Mail: Similarly, use the "More" menu to "Export" or "Download" the message as an .eml. Proton Mail emphasizes security, so downloading the file allows you to re-encrypt it if necessary when sending it to an external recipient.

Why Attaching an Email is Superior to Forwarding

While forwarding is the default behavior for most users, attaching an email as a file is a superior practice in professional and technical environments for several reasons.

Preservation of Headers and Metadata

When you forward an email, your email client creates a new message and "quotes" the old text. This process often strips away the original routing headers (which show the IP addresses and servers the mail passed through) and technical metadata. For IT security teams investigating phishing or for legal teams establishing a chain of custody, these headers are vital. Attaching the email preserves every byte of the original data.

Maintaining Original Formatting and Attachments

Inline forwarding often breaks HTML layouts, displaces images, and loses the original attachments that were part of the first email. By sending the message as an .eml file, the recipient opens a perfect replica. If the original email had a PDF invoice attached to it, that PDF remains inside the .eml file, keeping the "package" together.

Professionalism and Clarity

In complex projects involving dozens of stakeholders, a forwarded thread can become a "wall of text" that is difficult to navigate. Attaching separate emails allows you to say, "Please see the attached three emails for the client's previous approvals," which keeps your current message clean and allows the recipient to open the references in separate windows for side-by-side comparison.

Workarounds for Mobile Devices (iOS and Android)

The Gmail and Outlook mobile apps currently do not support attaching one email to another as a native .eml file. This is a significant limitation for professionals on the go. However, there are two effective workarounds.

The Print to PDF Method

Since almost every smartphone supports "Print to PDF," you can use this to create a readable version of an email that can be attached to a new message.

  1. Open the email in your mobile app (Gmail, Outlook, or Mail).
  2. Tap the "More" menu or the "Share" icon.
  3. Tap "Print."
  4. When the print preview appears, use the "Share" icon again or select "Save as PDF."
  5. Save the file to your phone's storage.
  6. Start a new email and attach the PDF you just created.

While this doesn't preserve the metadata like an .eml file does, it is the best way to share the visual content and text of an email while mobile.

Using a Mobile Browser in Desktop Mode

If you absolutely must send an .eml file from your phone, you can bypass the app restrictions:

  1. Open Chrome or Safari on your phone.
  2. Go to gmail.com or outlook.com.
  3. In your browser settings, select "Request Desktop Site."
  4. Use the web interface as described in the desktop sections of this guide. It will be small and difficult to navigate, but the "Forward as attachment" and "Download" features will be available.

Technical Details: .eml vs .msg Files

Understanding the file formats used during this process can prevent compatibility issues for your recipients.

  • .eml (Email Message): This is the industry standard. It was developed by Lotus and is now used by Gmail, Apple Mail, and almost every other client. If you aren't sure what your recipient uses, send an .eml file.
  • .msg (Outlook Message): This is a proprietary Microsoft format. While extremely powerful for Outlook users (it can even preserve "Flags" and "Categories"), it is often unreadable for people using Gmail or Mac Mail without specialized viewer software.

When using Outlook Desktop, if you want to ensure the best compatibility, it is often better to drag the email to your desktop first (which often saves it as .msg) and then convert it, or use the Outlook Web version to generate an .eml file instead.

Common Issues and Troubleshooting

Even with the correct steps, you might encounter hurdles when attaching emails.

File Size Limits

Emails are not designed to be a file transfer service. Most providers, including Google and Microsoft, have a 25MB limit for the total size of an email. If you attach five emails, and each of those original emails had a 10MB attachment, your new email will exceed the 50MB mark and fail to send.

  • Solution: In Gmail, if the attachment exceeds 25MB, it will automatically be uploaded to Google Drive, and a link will be inserted. In Outlook, you may receive an "Attachment too large" error. In these cases, it is better to download the original attachments and share them via a cloud service like OneDrive or Dropbox.

Security Banners and Phishing Warnings

When you receive an attached email, Gmail often displays a warning banner stating, "This attached email has not been verified." This is a standard security measure because email clients cannot verify the sender's identity of an attached file as easily as they can for a direct message.

  • Advice: If you are the sender, always include a brief note in the body of your message explaining what the attachments are. This builds trust and ensures the recipient doesn't delete your message as a potential security risk.

Opening Attached Emails on Mobile

Recipients using mobile devices may have trouble opening .eml or .msg attachments. While the Gmail app has a built-in viewer, other apps might require a third-party ".eml viewer" from the App Store or Play Store. If you know your recipient is primarily a mobile user, the PDF workaround mentioned earlier is often the more considerate choice.

Conclusion

Attaching an email to another email is a vital skill for anyone working in a professional digital environment. Whether you use Gmail's "Forward as attachment" feature, Outlook's "Attach Item" menu, or the flexible drag-and-drop methods, you are ensuring that your communication is clear, context-rich, and technically sound. By preserving the original metadata and formatting through .eml files, you provide a level of transparency that standard forwarding cannot match. While mobile devices still require workarounds like PDF conversion, the desktop experience is streamlined across all major platforms.

Frequently Asked Questions (FAQ)

How many emails can I attach to a single message?

Technically, there is no limit to the number of emails you can attach, as long as the total size of the draft does not exceed your provider's limit (usually 25MB). You can select 50 emails in Gmail and forward them all at once as a bulk attachment.

Can I attach a draft email to another email?

No, most clients require an email to be "Sent" or "Received" (i.e., having a completed header) before it can be attached. If you need to share a draft, it is better to copy the text or take a screenshot.

Will the recipient see if I have read the attached email?

No. Attaching an email sends a static copy of the message at that specific moment. Any further actions you take on the original email in your inbox (like marking it as read, deleting it, or flagging it) will not be reflected in the attachment sent to the recipient.

Does attaching an email include its original attachments?

Yes. When you attach an email as an .eml or .msg file, it acts as a container. Everything that was part of that original message—including the text, images, and any files attached to it—is included inside the new attachment.

How do I open an .eml file I received?

If you are on a computer, simply double-clicking the file should open it in your default email client (Outlook, Mail, or Thunderbird). In Gmail's web interface, you can click the attachment to open a preview window directly in your browser.