Emailing an attachment works the same across almost every service: click the paperclip icon in your compose window, pick the file, and hit send.
The paperclip icon is the universal signal for attaching a file in email, whether you’re using Gmail on a laptop or the Mail app on an iPhone. A single wrong tap can send a blank message or bounce a file that’s too large, but the actual process takes about ten seconds once you know where to find the right button. The table below shows how each major platform handles the basic attach step so you can skip the hunting.
How to Attach a File on Desktop (Outlook, Gmail, and Universal Steps)
Desktop email clients share the same basic workflow: open a new message, find the attachment button, select the file, and send. The platform-specific details differ slightly in where the button lives.
Microsoft Outlook
Open Home and click New Email. In the new message window, select Home then Attach File from the ribbon bar. Choose Browse This PC for local files, or select Attach Item and then Outlook Item to attach an actual email as a native Outlook message. Pick the file and click Insert. The attachment appears in the message header before you send.
Gmail in a Browser
Click Compose to open a new message window. At the bottom of the compose window, click the paperclip icon (labeled “Attach files” on hover). Navigate to the file in the system dialog and click Open. The file shows up as a chip at the bottom of the email. To attach a received email as a .eml file, drag and drop that email directly from your inbox into the compose window.
Universal Desktop Method
- Click New or Compose to start a message.
- Write the subject line and a short body explaining the file.
- Click the paperclip icon (usually in the toolbar at the top or bottom of the compose area).
- Browse your files, select the attachment, and click Open or Insert.
- Click Send.
How to Email an Attachment from a Phone or Tablet
Mobile email apps hide the attach option behind the same paperclip. On iOS and Android it just lives on a different part of the screen.
In the compose window, tap the arrow icon on the keyboard bar to expand the formatting options. Tap the paperclip icon, then select the file source — Files on iOS, or Documents/Storage on Android. Navigate to your file and tap it. The attachment appears as a bar at the bottom of the message. Tap Send and you’re done.
The the file’s name and size appear in the message before you hit send. If nothing shows up, the attachment didn’t take.
Size Limits That Matter in 2026
The total message — body text, headers, signatures, inline images, and the attachment itself — cannot exceed 20 to 25 MB on most major providers like Gmail, Outlook, and Yahoo. The attachment isn’t the only thing counted.
The safe thresholds break down like this:
| File Size | What to Do | Risk Level |
|---|---|---|
| Under 1 MB | Attach directly | Safe |
| 1 MB – 5 MB | Attach directly | Low risk |
| 5 MB – 10 MB | Attach, but verify the full message stays under 25 MB | Caution needed |
| Over 10 MB | Use a cloud link (Google Drive, OneDrive) instead | High risk of bounce |
Most providers now insert a cloud link automatically when they detect a large attachment during upload. If your file is over 10 MB, it’s safer to upload it to Drive or OneDrive first and paste the share link into the email body with a note explaining what the link opens.
What Formats Work Best (So the Recipient Can Open It)
The format you choose determines whether the other person gets a readable file or a scrambled mess. Stick with universal types for the widest compatibility.
- Documents: PDF beats Word every time. A PDF preserves your layout, fonts, and formatting on any device or OS.
- Images: JPEG and PNG work on every email client and phone gallery app.
- Audio and Video: MP3 for audio, MP4 for video. Both play natively on nearly everything.
- Email messages: Gmail converts dragged emails to .eml files; Outlook uses native Outlook items when you choose Attach Item > Outlook Item.
How to Attach an Email Message to Another Email
Forwarding is not the same as attaching. When you attach a message, the original email arrives as a standalone file the recipient can open and save. The method depends on your client.
In Gmail, drag the email from your message list directly into an open compose window — it attaches as a .eml file. In Outlook, click Attach Item > Outlook Item while composing, then select the email from your folder list. In Apple Mail on a Mac, drag the email from the message list into the body of your new email — it attaches as a .eml file there too.
Eight Mistakes That Break an Attachment Email
Most attachment problems are avoidable with a quick double-check before hitting send.
| Mistake | Why It Hurts |
|---|---|
| Vague subject line | Emails with subjects like “Attachment” or “Document” get lost in crowded inboxes. |
| Oversized file sent directly | Large files bounce the whole message back to you. |
| Pasting text instead of attaching | Copy-pasting document text loses the file’s formatting and structure. |
| No message in the body | The recipient has no context for why you sent the file. |
| No virus scan before attaching | Receivers block suspicious files; some providers auto-reject unverified ones. |
| Inaccessible file design | Untagged PDFs and images without alt text can’t be read by screen readers. |
| Wrong file format | A .pages file sent to a Windows user is unopenable without conversion. |
| Forgetting the attachment | Hitting send with “see attached” in the text and nothing on the message. |
The Attach-and-Send Checklist
Run through this sequence before every attachment email to catch the most common failures.
- Compose a new message with a specific subject line — “Q3 Report — Attached PDF” instead of “Attachment.”
- Write one or two sentences in the body explaining what the file contains and why you’re sending it.
- Click the paperclip icon and select your file.
- Check the file size — if it’s over 5 MB, confirm the total message won’t exceed 25 MB. Over 10 MB means switch to a cloud link.
- Confirm the format — PDF for documents, JPEG for images, MP4 for video.
- Verify the attachment appears in the compose window before you click send.
- Add the recipient email, double-check the address, and click Send.
The attachment bar or chip in the compose window is your guardrail: if you see it, you’re good. If you don’t, go back and re-select the file before you click send.
References & Sources
- Southwest. “SMTP2GO — The Goldilocks Theory of Email File Sizes (2026)” Covers the 20–25 MB total message limit across major providers.