How to test authentication and deliverability of your outgoing email?

Updated: 28 September 2026 · Applies to: Email sent from your own server

Before you send to real recipients, and regularly after that, test how your mail looks to the receivers: does authentication pass, is the sending address recognised, and what do the big providers say about your reputation. This guide shows the quickest tests, and how to set up Google Postmaster Tools.

1. Read the headers of a test message

1. Send a message from your server to a Gmail address you own (How to install and configure Postfix for sending on Ubuntu?, step 4).
2. Open the message, click the three dots and choose Show original.
3. At the top Gmail shows SPF: PASS, DKIM: PASS and DMARC: PASS with the domain. All three must pass.
4. In the headers find the first Received: line. It must show the HELO name and the IP address of the sending address you intended (How to make Postfix send from a specific IP address with a matching HELO name?).
5. Look for List-Unsubscribe and List-Unsubscribe-Post for marketing messages (How to add a working unsubscribe link and one-click unsubscribe headers to your emails?).

Do the same with a free Outlook.com or Yahoo mailbox to see how their systems treat the message; their "view message source" options show the Authentication-Results header.

2. Test from every sending address

If you use several addresses, test each one with a separate message from each domain that uses it (How to give each domain or customer its own sending IP address in Postfix?). A problem often affects only one address.

3. Check DNS

dig -x YOUR-IP +short
dig +short A mail1.example.com
dig +short TXT example.com
dig +short TXT s2026._domainkey.example.com
dig +short TXT _dmarc.example.com
sudo opendkim-testkey -d example.com -s s2026 -vvv

4. Set up Google Postmaster Tools

Google Postmaster Tools shows Gmail's view of your domain: the spam rate, the reputation of your domain and IP addresses, and authentication results. Gmail asks bulk senders to keep the spam rate below 0.3%.

1. Open postmaster.google.com and sign in with a Google account.
2. Add your sending domain and verify it with the TXT record that Google gives you. On cPanel hosting see How to Add an MX Record in cPanel DNS Zone Editor for adding records; the record type is TXT, and the name is the domain itself.
3. Wait. The dashboards show data only after enough mail has been sent to Gmail users, so a small test volume shows nothing yet.
4. Check the spam rate and authentication graphs regularly, especially while you warm up (How to warm up a new sending IP address step by step?).

5. Other providers

• Yahoo Sender Hub (senders.yahooinc.com): sender information, best practices and the complaint feedback loop for senders who sign their mail with DKIM.
• Microsoft sender support (sendersupport.olc.protection.outlook.com): information for Outlook.com senders and programmes such as SNDS.

6. Watch the results of real sending

• Delivery log counts: sent, deferred, bounced (How to read Postfix logs and understand common SMTP error codes?).
• Your newsletter tool's reports: opens, clicks, unsubscribes, complaints.
• The automatic checks in How to monitor your sending IP addresses automatically with a script?.

If a test fails

• SPF fail: the sending address is not in the record (How to write an SPF record for a server with several IP addresses?).
• DKIM fail or none: no signature, or a wrong record (How to set up DKIM signing with OpenDKIM and Postfix for several domains?).
• DMARC fail: neither SPF nor DKIM passes with a matching domain (How to publish DMARC for your sending domains and tighten the policy safely?).
• Message in spam although all pass: the address is new (warm up slowly), or the content or list has a problem.

Frequently asked questions

How often should I test?
After every change to DNS or to the mail server, and once a month as a routine.

Are there online tools that test a message for me?
Yes, several. Use them as a second opinion; the headers and Postmaster Tools are the results that count.

Sources: Google: Email sender guidelines.

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