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Why mail lands in spam

Receivers such as Gmail and Microsoft decide where each message goes by weighing many signals. Some you control in DNS. Most come from how you send.

Authentication: the entry ticket

Without SPF, DKIM and DMARC, much of your mail won't reach the inbox at all. Since 2024 Gmail and Yahoo, and since 2025 Outlook.com, require domains that send in bulk to have all three, with mail aligned to the From address, plus a one-click unsubscribe on marketing mail. This is the part healthcheck.email checks.

Reputation: your track record

Receivers remember how people react to your mail. Complaints ("report spam") hurt the most: keep them well under 1 in 1,000. Mail to addresses that don't exist, and sudden jumps in volume, hurt too.

List hygiene

  • Send only to people who asked for your mail.
  • Remove addresses that bounce.
  • Let people unsubscribe easily, and honor it right away.
  • Stop mailing people who haven't opened anything in months.

Content

  • Make it clear who it's from and why the reader is getting it.
  • Keep links pointing at domains you control.
  • Avoid sending one large image with no text.

Keep streams apart

Send newsletters from a different subdomain, such as news., from invoices and password resets. If marketing mail draws complaints, your important mail keeps its own reputation.

Blocklists and reverse DNS

Receivers also check public blocklists. If a server that sends your mail is on one, much of its mail goes to spam or is refused. A server with no matching reverse DNS name looks suspicious too.

We check the servers that are yours: the single addresses in your SPF record and the mail servers in your own domain. Servers that belong to your providers, such as Google or Mailchimp, carry the provider's reputation, and the provider looks after it. We also check your domain against a domain blocklist. When a list won't answer us, the report says we couldn't check it. That isn't the same as being listed.

In healthcheck.email

Your report's first two questions, "Does your email work?" and "Can someone pretend to be you?", cover the authentication part, and a listed server or domain shows up under the first. For the rest of reputation, the major mailbox providers offer free dashboards, such as Google Postmaster Tools.