THE MAIL TROUBLESHOOTING FIELD GUIDE

Read the Evidence Behind Email Delivery.

A bounce is a starting clue. It is not always a blocklist problem, and a published DNS record is not always proof that a message authenticated.

01 / MAIL ROUTING

Read the Mail DNS.

MX preference, null MX, SPF and exact-name DMARC—with important boundaries.

5 min read 02 / SENDING REPUTATION

Understand a Blocklist Result.

Listed, not listed and unknown mean different things. Know which IP to test and how to seek a review yourself.

7 min read 03 / IN THE FIELD

Work Through a Bounce.

Follow a practical checklist before changing DNS or requesting delisting.

5 min read

Start with the Right Question

Question	Useful Check	What It Does Not Prove
Where should incoming mail go?	Mail DNS → MX	That an SMTP server is reachable or a mailbox exists.
Is a sender policy published?	Mail DNS → SPF / DMARC	That a particular message passes authentication.
Is this sending IP on SpamCop?	Sending IP → IPv4	That every receiver or every blocklist agrees.
Does this IP have a PTR name?	Sending IP → Reverse DNS	That forward DNS matches, or that the name identifies a trustworthy sender.

Keep Your Evidence Small and Specific

Record the time, recipient-provider response code, sending IP and relevant domain. Remove recipient addresses, message content and tokens before sharing a report. The tool needs a public domain or IP, not the entire message.

Know the Coverage

The site inspects three DNS questions for a domain. For a public IPv4 address it queries one blocklist, verifies access with positive and negative controls, and looks up PTR data. IPv6 currently receives a PTR check only. There is no hidden multi-list scan, SMTP login, message sending, automatic remediation or scheduled monitoring.