Short answer: To see every header of an email in Mail on a Mac, select the message and choose View > Message > All Headers (Shift-Command-H). For the complete original message, choose View > Message > Raw Source (Option-Command-U). To always show one or two extra fields, such as Return-Path or Reply-To, go to Mail > Settings > Viewing, set Show message headers to Custom and add them.
The steps below are for macOS 27 and match macOS Tahoe 26, Sequoia 15 and Sonoma 14. Showing headers changes only what you see. It doesn't change the email or anything you send.
What message headers are
Every email carries a block of header fields above the text. Mail normally shows a short version: who sent it, who it went to, the subject and the date. The full set is much longer and records the route the message took, where replies go and whether the sender's domain passed authentication checks. The format is defined in RFC 5322.
| Header | What it tells you |
|---|---|
| From | The sender as shown to you. Easy to fake, so don't trust it alone. |
| Reply-To | Where your reply goes if it differs from From. A mismatch is worth a second look. |
| Return-Path | The address that bounces go back to, set during delivery. |
| Received | One line per server that handled the message. Read them from the bottom up to trace the route. |
| Message-ID | A unique ID for the message, handy when asking a provider to trace it. |
| Authentication-Results | Whether the message passed SPF, DKIM and DMARC checks at your provider. |
| List-ID / List-Unsubscribe | Shows a message came from a mailing list, and how to leave it. |
Our guide to reading email headers goes through each field in more detail.
How to view all headers in Apple Mail
- Open Mail and select the message.
- Choose View > Message > All Headers, or press Shift-Command-H.
- The header area above the message expands to show every field.
- To go back to the short version, choose View > Message again and turn the option off (in some versions the item reads Default Headers).
How to view the raw source of an email
Raw Source shows the whole message exactly as it arrived: every header plus the encoded body and attachments. It's what a provider's support team or an email header analyzer asks for.
- Select the message.
- Choose View > Message > Raw Source, or press Option-Command-U. The source opens in its own window.
- Select the text you need and copy it.
To keep a copy as a file, choose File > Save As and pick Raw Message Source as the format. Mail saves it as an .eml file, which you can attach to a support request. Dragging a message to the desktop does the same.
Show custom header fields every time
If you check the same field often, you can make Mail show it on every message without opening All Headers.
- Choose Mail > Settings, then click Viewing.
- Click the pop-up menu next to Show message headers and choose Custom.
- Click the Add (+) button and type the name of the header, such as Return-Path, Reply-To or List-ID.
- Click OK. The field now appears in the header of every message that has it.
To undo it, open the same setting and choose Default. Older guides send you to Mail > Preferences; in current macOS the menu item is Mail > Settings.
This is about what you see. Mail doesn't let you add your own custom header fields to messages you send. It does let you show extra address fields when you write, such as Bcc and Reply-To, from the View menu in a new message.
Use headers to check a suspicious email
Headers are the quickest way to tell whether a message really came from who it claims to be. Open All Headers and look at three things:
- Authentication-Results: look for
spf=pass,dkim=passanddmarc=passfor the sender's domain. A fail on a message claiming to be from your bank is a red flag. The field is defined in RFC 8601. - Reply-To: if it points to an address unrelated to the sender, replies go to someone else.
- Received: the bottom line shows where the message entered the mail system.
Our guide to spotting phishing emails covers the other signs. If a message is junk, move it to Junk rather than replying; see junk mail settings in Mac Mail.
Viewing headers on iCloud.com
If you're away from your Mac, iCloud Mail on the web can show headers too: select the message on icloud.com/mail, open its options menu and choose Show All Headers. Choose Show Default Headers to hide them again.
Want an inbox that sorts itself?
Disclosure: we make Canary Mail. If you check headers because you worry about phishing, it may help to have an app that flags suspicious mail for you. Canary Mail is an email app for Mac, iPhone, iPad, Windows and Android that works with Gmail, Outlook, iCloud, Yahoo, Exchange and other IMAP accounts. The free plan covers unlimited accounts on 2 devices with AI inbox sorting, and the triage runs on your device. Tracker blocking is on by default, and your email isn't used to train AI. The Pro+ plan ($100 a year) adds phishing and impersonation detection and PGP encryption. More than 2 million people use it, and Apple has featured it on the App Store and the Mac App Store.
Frequently asked questions
How do I see full email headers in Apple Mail on a Mac?
Select the message and choose View > Message > All Headers, or press Shift-Command-H. Choose the same item again to go back to the short header.
How do I view the source of an email in Mac Mail?
Choose View > Message > Raw Source, or press Option-Command-U. The full source opens in a separate window, where you can copy it.
How do I always show the Reply-To field in Mail?
Go to Mail > Settings > Viewing, set Show message headers to Custom, click Add and type Reply-To. It then shows on every message that has a Reply-To address.
Can I change the header of an email I send in Apple Mail?
Only the visible parts. You can show the Cc, Bcc and Reply-To fields from the View menu while writing, but Mail has no option to add custom technical header fields to outgoing mail.
How can I analyze email headers?
Copy the raw source (View > Message > Raw Source) and read the Authentication-Results and Received lines, or paste the headers into a header analyzer tool. Our email headers guide explains each field.
More Mac Mail guides
- How to sort messages in Mac Mail
- How to unsubscribe from emails in Mac Mail
- How to archive emails in Mac Mail
- Junk mail settings in Mac Mail
- Email headers explained
- How to spot phishing emails
Other Mac Mail fixes
- Mac Mail not opening or freezing
- Mac Mail keeps crashing
- Mac Mail not sending emails
- Messages stuck in the Outbox
- Mac Mail not receiving emails
- Mac Mail inbox not updating
- Mac Mail can't connect to the server
- "Unable to verify account name or password"
- Mac Mail not showing attachments
- Mac Mail not showing images
- Mac Mail search not working
Sources
- Apple Mail User Guide (macOS Sequoia): Show detailed headers
- Apple Mail User Guide (macOS 27): Change Viewing settings
- Apple Mail User Guide (macOS 27): Keyboard shortcuts
- Apple Mail User Guide (macOS 27): Delete emails and manage storage
- Apple: View all email headers in Mail on iCloud.com
- RFC 5322: Internet Message Format
- RFC 8601: Message Header Field for Indicating Message Authentication Status