Your test email address

Every workspace has one permanent test address, and it looks like this: yourbusiness-742@checkinboxdecay.com. The first part comes from your primary domain, so you can recognize it in a subscriber list months later; the digits keep it unique. It lives on checkinboxdecay.com, a domain we run purely for receiving these emails, and it never changes for the life of your workspace.

The instruction that comes with it is one sentence: add this address to every mailing list you send, and send a test email (or a real campaign) from each tool you use.

Why an email address at all

DNS can tell us how your domain is configured. Only a real email can tell us how your mail actually travels. When your campaign arrives at the test address, its headers carry the evidence mailbox providers grade you on: which IP sent it, which domain signed it, whether SPF and DKIM passed, how DMARC evaluated, whether the connection was encrypted, whether the unsubscribe headers Gmail and Yahoo now require are present.

None of that is visible from the outside. It only exists in a delivered message, which is why sending one test email per tool is the entire setup.

What happens when an email arrives

Within moments of arrival we parse the headers and run the path-level checks. Three things can happen, all automatic:

• A new sending path appears if this is a route we haven't seen before, scored per check.
• Any domain the email reveals that belongs to you (the visible From domain, and bounce or signing domains under an apex you track) is added to your domain list and checked.
• You get an email: we got it, here's what we found.

The email itself is kept as evidence. Its report shows the authentication results plus a free content snapshot: size and structure, image-to-text balance, link analysis, and whether the unsubscribe basics are present.

Good habits

Send from the tool, not from your inbox. A test broadcast from Mailchimp travels Mailchimp's route; a message you write in Gmail travels Google's. Both are useful, but only if you know which one you're testing.

If you use one tool for newsletters and another for receipts or cold outreach, send from each. Different tools take different routes, and it is entirely normal for one path to be healthy while another is quietly failing. That per-tool picture is the point.

Leaving the address on your lists permanently is deliberate: every future campaign then refreshes the evidence without you thinking about it.

More in Getting started

• Getting started: from signup to your first verdict
• Adding and managing domains