What you’ll need
- A test message that didn’t arrive properly, or its bounce
- A Gmail or Outlook.com account to test with
- DNS lookup tools
Delivery problems have many possible causes. This tutorial narrows them down in order, so you fix the actual cause rather than guessing.
Steps
Step 1: Classify the problem
Pick one: the app won’t send (Can’t send email: how to fix outgoing mail), it bounces (continue), it vanishes (continue), or it arrives in spam (continue from step 3).
Step 2: Read the bounce
If there’s a bounce, find the status code and reason.
5.7.xcodes usually mean authentication or policy;listed atmeans a blocklist;user unknownmeans a wrong address. Understanding email bounce messagesStep 3: Send a controlled test
Send a short plain message, no links or attachments, from the affected mailbox to your Gmail test account. Plain content rules out content filtering.
Step 4: Read the authentication results
In Gmail, Show original. Record SPF, DKIM and DMARC results. Anything other than PASS: fix it first with Set up SPF, DKIM and DMARC.
Step 5: Check the headers for the sending path
In the original message, read the
Received:lines from the bottom up. The first one added by your server shows the sending IP. Confirm mail left through your Traxio server rather than another service.Step 6: Check reputation
Look up the sending IP and your domain on a multi-blocklist checker. Note which lists, if any. Email blacklists (blocklists): how to check and what to do
Step 7: Test with content
Send your real message — with its links, images and signature — to the same test account. If the plain test lands in the inbox but the real one doesn’t, the content is the problem: links, a URL shortener, a heavy image or wording.
Step 8: Check for account compromise
Look in the mailbox’s Sent folder and your forwarders for anything you didn’t create. My email account is sending spam
Step 9: Escalate with evidence
If authentication passes, content is clean and the server IP is listed on a major blocklist, send the help desk the bounce, the headers and the list name.
Check it worked
You can state which of these is the cause — authentication, content, reputation, recipient address or account compromise — and the controlled test now reaches the inbox.
If something goes wrong
| What happens | What to do |
|---|---|
| Only Microsoft addresses affected | Microsoft filters heavily on reputation. Keep authentication perfect and ask recipients to mark you as safe while reputation builds. |
| Only website forms affected | The form sends unauthenticated or with the visitor as From. Sending email from your website reliably |