Every email carries a set of hidden technical details, its header, that most people never look at. Yet this information can explain why a message ended up in spam, confirm whether a sender is who they claim to be, and help you troubleshoot delivery problems. Here's what an email header is, why it matters, and exactly how to view one in Outlook.
What Is an Email Header?
An email header is the technical metadata attached to every message, separate from the subject line and body you normally see. It records the sender and recipient addresses, the timestamp, and the path the message took across mail servers to reach your inbox. Email systems use this information to route the message correctly and to check whether it's authentic.
Key Components of an Email Header
- From - the sender's email address
- To - the recipient's email address
- Subject - the message title
- Date - when the message was sent
- Message-ID - a unique identifier for tracking the message
- Received - the record of mail servers the message passed through
- Return-Path - where bounce-back notifications are sent
- Authentication-Results - whether the message passed SPF, DKIM, and DMARC checks
Why Email Headers Matter
Diagnosing Delivery Problems
If a message never arrives, or lands in spam, the header often explains why, whether that's a missing authentication record or an issue at a particular mail server along the route.
Validating Legitimacy
Comparing the sender's domain, the path it traveled, and the authentication results helps you tell a genuine email apart from a phishing attempt.
Strengthening Security
Because headers capture verification details, reviewing them regularly on suspicious messages adds another layer of protection against fraud.
Understanding Delivery Performance
For anyone sending email regularly, headers provide a clear record of exactly when and how messages were delivered.
How to View an Email Header in Outlook
Outlook Desktop (Windows)
- Open the email you want to inspect.
- Click the three dots (More options) in the upper-right corner of the message.
- Select View Message Source.
- Review the header details displayed in the new window.
Outlook on the Web (Office 365 or Outlook.com)
- Open the message in your inbox.
- Click the three dots in the upper-right corner of the message.
- Select View Message Source.
- Review the header text that appears in the new window.
Outlook on Mac
- Open the message you want to inspect.
- Click View in the top menu.
- Select Message Source.
- Review the full header details in the window that opens.
What to Look For Once You've Opened the Header
- Received fields - trace the route and spot delays
- Authentication results - look for SPF, DKIM, and DMARC failures
- Return-Path - check that it matches the sending domain
- Message-ID - confirms a unique, traceable message
- Sender information - make sure the From domain matches what it claims to be
Common Questions
Why can't I find "View Message Source" in my version of Outlook?
Menu wording can vary slightly between Outlook versions and updates. Look for options like View, More actions, or the three-dot menu near the top of an open message.
Do I need to check headers on every email I receive?
No. It's most useful for messages that seem suspicious, ask for sensitive information, or fail to arrive as expected.
What's the quickest sign that an email might be fraudulent?
A mismatch between the From address and the Return-Path, or a failed SPF/DKIM authentication result, are both strong warning signs.
