How to test email deliverability without guessing

Decide what the test needs to answer

“Is our email healthy?” is too broad to be a useful test question. Narrow it to a specific route, message and outcome. For example: “Does our CRM-generated interview update authenticate?” or “Does our client-outreach message reach these test mailboxes?”

If the message will not send, start with the sending system and its error. A placement test cannot inspect a message that never leaves the sender.

Match the check to the job

Our header explainer is a local reading aid. It is not a DNS checker or a cryptographic verifier.

Send through the actual route

A message sent directly from Outlook is not an equivalent test of a CRM automation that uses another service. Use the route, sender identity, links and message type you need to investigate.

Keep a note of the sending account, platform, test time and message version. If a test service asks you to insert an identifier or use a particular procedure, follow that service’s current instructions. Do not assume forwarding a received message preserves the original test conditions.

Use accounts and test destinations you are authorised to use. There is no need to send candidate or customer information in a diagnostic message.

Start with the low-cost checks

If you already have a genuine affected message, examine its headers and any error first. An obvious authentication failure or sending restriction may give IT a more direct starting point than a paid placement report.

Mail-tester and MXToolbox are examples of services that cover parts of message and DNS investigation. Check their current free allowances and what each result actually measures.

GlockApps can be relevant when you need provider-level placement observations and repeatable seed tests. See GlockApps and its current testing options . A free allowance or small credit pack may be enough for an occasional check; an ongoing subscription should have an ongoing purpose.

Read the report by provider

An overall percentage can conceal a useful pattern. Look at the individual receiving providers and any missing messages. Separate personal accounts from business mailbox environments when evaluating relevance to your audience.

For a recruitment agency, candidate messages may go to personal accounts while client outreach goes to managed business domains. A personal Outlook.com seed is not a model of every Microsoft 365 organisation’s policy.

If two services disagree, examine the mailbox environments and test conditions before deciding which number to believe. Keep the disagreement in your notes.

Retest with a controlled comparison

Save a baseline. Make one justified change. Then repeat a comparable test and record the conditions. You are looking for evidence that the change did what you intended, not a score that looks reassuring.

A successful seed result is a useful observation about that test. Continue to monitor genuine rejection evidence and recipient feedback. Don’t replace real outcomes with an isolated green dashboard.

Pick tools by use case

Choose a product for the question it can answer, the relevant mailbox coverage, understandable reports and the frequency you actually need. Our testing-options guide compares categories and documented capabilities without pretending we have run a head-to-head experiment.