An email header is a section of an email that contains important metadata about the message, including information on the sender, recipient, the servers the email passed through, and other technical details that help route the email to its destination. The email header is usually hidden from view in most email clients, but it can be accessed to troubleshoot issues like email delivery failures, spam filtering, and authentication.
Key Sections of an Email Header:
Here are the most important sections of an email header and how you can use them to improve deliverability:
1. From:
Description: The email address of the sender.
How It Affects Deliverability: Ensure that the "From" address is recognizable and consistent with your domain. Using an email address that aligns with your business domain (rather than a free email service like Gmail or Yahoo) improves deliverability and builds trust.
Action: Use a domain-based email (e.g., [email protected]) rather than a freemail service (e.g., @gmail.com).
2. To:
Description: The recipient's email address.
How It Affects Deliverability: Make sure you're sending emails to valid, correctly formatted addresses. Invalid or mistyped addresses increase bounce rates, damaging your sender reputation.
Action: Clean your email list regularly using an email validation tool to reduce bounces and ensure you’re sending to valid addresses.
3. Return-Path:
Description: The email address where bounce messages (non-delivery reports) are sent. This is the actual sender's address used for email bounce handling, often set by the email service provider (ESP).
How It Affects Deliverability: The return path should match your domain, as mismatched return paths can raise suspicion with receiving mail servers.
Action: Ensure that the Return-Path domain matches your sending domain. If you’re using a third-party ESP, verify that they are properly handling your return-path records.
4. Received:
Description: This shows the servers that processed the email as it was sent to the recipient. Each time the email passes through a server, it adds a "Received" line, starting with the most recent one.
How It Affects Deliverability: Reviewing these entries helps identify the email’s journey and detect any possible delays or issues caused by intermediary mail servers. It also shows if the email was sent from a legitimate server that’s listed in your SPF record.
Action: Check the chain of "Received" entries to ensure emails are coming from authorized servers and that they align with your SPF record.
5. Message-ID:
Description: A unique identifier for each email. It is used to track emails and is typically generated by the email client or server.
How It Affects Deliverability: Emails with invalid or missing Message-IDs can trigger spam filters. Some mail services require correctly formatted and unique Message-IDs.
Action: Ensure your email server generates valid and properly formatted Message-IDs for each outgoing email.
6. DKIM-Signature:
Description: Shows the DomainKeys Identified Mail (DKIM) signature, which is used to verify the email's authenticity. It includes details like the domain used for signing, the selector, and the hash of the email body.
How It Affects Deliverability: A valid DKIM signature shows that the email has not been altered during transit and comes from an authorized sender. Failing DKIM checks can lead to emails being flagged as spam.
Action: Ensure DKIM is properly set up for your domain. This involves creating a DKIM TXT record in your DNS settings and verifying that emails are correctly signed by your mail server.
7. SPF:
Description: Information related to the Sender Policy Framework (SPF) check. It confirms whether the sending server is authorized to send email on behalf of the domain.
How It Affects Deliverability: SPF checks failing means the email came from an unauthorized server, which can lead to deliverability issues or the email being marked as spam.
Action: Make sure your SPF record is correctly configured in your domain’s DNS settings, listing all authorized servers that can send email on your behalf.
8. DMARC:
Description: The Domain-based Message Authentication, Reporting & Conformance (DMARC) policy that indicates how an email server should handle SPF and DKIM failures (e.g., reject or quarantine).
How It Affects Deliverability: DMARC provides additional instructions to mail servers about handling authentication failures and helps prevent email spoofing. It also allows you to receive reports on authentication results.
Action: Implement a DMARC policy and monitor reports to understand how your emails are being authenticated across different mail servers.
9. X-Spam-Status:
Description: Indicates whether the email has been flagged as spam by a spam filter (e.g., SpamAssassin) and what score it received.
How It Affects Deliverability: If the spam score is high, the email is likely to end up in the recipient’s spam folder or be rejected.
Action: Analyze the spam score and the rules that triggered it to identify problematic content, such as spammy keywords, bad formatting, or suspicious links. Adjust your email content accordingly.
10. MIME-Version and Content-Type:
Description: These fields define the format of the email and the type of content it contains (e.g., text, HTML, attachments).
How It Affects Deliverability: Incorrect or inconsistent MIME settings can cause the email to render improperly, or worse, be flagged as spam.
Action: Ensure that your emails are properly formatted with both plain text and HTML versions, and use well-structured MIME formatting.
11. Authentication-Results:
Description: Provides the results of various authentication checks (SPF, DKIM, DMARC, etc.) performed by the recipient’s mail server.
How It Affects Deliverability: This field tells you whether your email passed or failed these critical authentication checks. Failing any of these checks can cause your emails to be rejected or classified as spam.
Action: Monitor this field to ensure your emails consistently pass SPF, DKIM, and DMARC checks. Fix any issues if authentication fails.
How to Use Email Headers to Improve Deliverability:
Ensure SPF, DKIM, and DMARC Pass:
Set up SPF, DKIM, and DMARC for your domain to ensure that receiving mail servers can authenticate your emails.
Regularly monitor the Authentication-Results field in email headers to check if your emails are passing these checks.
Use tools like MXToolbox or Google Postmaster to test and monitor these settings.
Monitor Spam Scores:
Check the X-Spam-Status header to identify why certain emails may be flagged as spam. Look at the specific spam filter rules that were triggered, such as certain keywords, suspicious links, or missing authentication.
Adjust your content based on this feedback (e.g., remove spammy keywords, add proper email formatting, and avoid excessive images).
Ensure Consistent Message-IDs:
Make sure your email system generates unique and properly formatted Message-IDs. Misconfigured Message-IDs can raise spam suspicions.
Analyze Email Routing (Received):
Use the Received headers to identify any delays or issues with the email’s journey across servers. This can help you spot issues with slow servers or unauthorized routing that may cause SPF failures.
Maintain a Valid Return Path:
Ensure that the Return-Path is valid and consistent with your sending domain. It should handle bounce messages correctly and be configured to handle feedback loops if needed.
Send Plain Text and HTML Versions:
Use the MIME-Version and Content-Type headers to ensure you are sending both a plain text and an HTML version of your email. Some mail clients or servers may flag HTML-only emails as suspicious.
By regularly reviewing email headers and making sure they comply with email authentication and best practices, you can significantly improve your email deliverability and avoid common issues that cause emails to end up in spam folders.