ZeroSpams

Fix emails going to spam

Quotes that customers never see. Invoices that end up in junk. Replies that "never arrived". When business email goes to spam, it costs sales quietly, and the cause is usually one of a handful of fixable problems.

Updated · 2 min read · By the ZeroSpams team

The short answer

Emails go to spam for a few main reasons: missing or broken SPF, DKIM or DMARC; a poor sender reputation or a blacklisted IP; sending from a website or tool that isn’t authorised for your domain; or content and sending habits that look like spam. Gmail and Outlook now reject or junk mail from domains that aren’t authenticated [1][2]. We test your email, find the cause, fix it and confirm it reaches the inbox.

What’s included

  • Test emails to Gmail, Outlook and other providers, with the full headers read, not guessed.
  • Authentication checked and fixed: SPF, DKIM, DMARC and alignment for every sending service.
  • Reputation: blacklist checks for your domain and IP addresses, and delisting where needed.
  • Sending setup: website email, CRMs and tools that send "as you" without being authorised.
  • Content and habits: what in your messages or sending patterns triggers filters.
  • A short report: the cause, the fix, and how to keep it from coming back.

How we do it

  1. Reproduce the problem with test emails to the affected providers.
  2. Read the headers: they state exactly why a message passed or failed.
  3. Fix the causes, in order of impact.
  4. Re-test until messages land in the inbox.
  5. Watch for a week to confirm it holds.

The usual culprits

  • No DKIM on your main email service, or on the tool that sends your quotes.
  • Your website sends email (contact form notifications, order emails) from a server that isn’t in your SPF record.
  • Two SPF records, or one with too many lookups, so SPF fails for everything.
  • A blacklisted IP on shared hosting, caused by another customer of the same host.
  • Bulk mail from the main domain: newsletters sent from the same domain as your daily email, dragging its reputation down.

Error messages that point to authentication

If your emails bounce with messages mentioning authentication, the cause is almost certainly SPF, DKIM or DMARC. Outlook uses "550 5.7.515" for domains that don’t meet its authentication requirements [2], and Gmail has been rejecting non-compliant bulk mail since November 2025 [1].

Common questions

Can you guarantee my emails will reach the inbox?

Nobody honestly can: Gmail and Outlook decide, based partly on how recipients react. What we can do is remove every technical reason for spam placement, and show you the test results.

Why do my emails reach some people but not others?

Each provider filters differently, and company mail servers have their own rules. That’s why we test to several providers, and read the headers from each.

How quickly can it be fixed?

DNS changes usually take effect within hours. Reputation problems, like a blacklist or a damaged domain reputation, can take days or weeks to recover.

Sources

Numbers in this guide come from these studies and publications. Links open the original.

  1. Email sender guidelines FAQGoogle Workspace Admin Help (Gmail)Requirements for senders of 5,000+ messages a day to Gmail since February 2024; stricter enforcement, including rejections, since November 2025.
  2. Strengthening Email Ecosystem: Outlook’s New Requirements for High-Volume SendersMicrosoft Defender for Office 365 blog, Microsoft Tech Community, 2025Since 5 May 2025: SPF, DKIM and DMARC required for domains sending 5,000+ emails a day to Outlook.com, Hotmail and Live.