# Why are my emails going to spam, and how do I fix it?

URL: https://iblockspam.com/blog/why-are-my-emails-going-to-spam
Last updated: 2026-10-09
Published: 2026-10-09
Topic: Running email day to day
Author: iBlockSpam Team

> Why your outgoing emails land in spam at Gmail or Outlook: authentication, alignment, spam complaints, blocklists, reverse DNS, new domains and forwarding.

## Short answer

Your emails usually go to spam because receivers can't verify them or don't trust the sender. Check that SPF or DKIM passes and aligns with your From domain, that DMARC exists, that your sending IP has reverse DNS and isn't blocklisted, and that recipients aren't marking your mail as spam. Gmail wants a spam rate under 0.3%.

When your own messages land in other people's spam folders, the fix is almost always on the sending side: in your DNS, your sending services or your sending habits. This guide is for senders. If you're the recipient trying to work out why a message reached your spam folder or quarantine, read [why did this email land in spam](https://iblockspam.com/blog/why-did-this-email-land-in-spam) instead.

## Is it going to spam, or being rejected?

Start by finding out what's actually happening, because the fixes differ.

- **Spam or Junk folder.** The receiver accepted the message but didn't trust it. You get no bounce. The causes in this guide apply.
- **Bounce.** The receiver refused the message during delivery, and you got a non-delivery report with a code such as `550 5.7.26`. Look the code up in our [SMTP error code lookup](https://iblockspam.com/tools/smtp-error-codes); each code page explains the cause.
- **Quarantine at the recipient's side.** The recipient's own filter held the message. Only they or their admin can release it, and it doesn't always mean your setup is wrong.

The quickest way to see what a receiver sees is to send one real message to our [Email Deliverability Test](https://iblockspam.com/tools/deliverability-test). It reports SPF, DKIM and DMARC results with alignment, your server's reverse DNS, blocklists, TLS and a spam verdict.

## What are the most common causes?

| Cause | Typical sign | Where to fix it |
|---|---|---|
| Missing or failing SPF or DKIM | `spf=fail` or `dkim=none` in the recipient's headers | DNS and each sending service |
| SPF or DKIM passes, but not for your domain | `dmarc=fail` despite a pass | Custom return-path or custom-domain DKIM |
| No DMARC record | `dmarc=none`; bulk mail refused | Publish DMARC |
| High spam-complaint rate | Gmail Postmaster Tools spam rate rising | List quality and sending practices |
| IP or domain on a blocklist | Bounces naming a list | Delisting, after fixing the cause |
| No reverse DNS on your own server | `550 5.7.25` from Gmail | PTR record at your IP provider |
| New domain or IP | Spam placement on first campaigns | Warm up gradually |
| Hidden or inconsistent links and content | Mail authenticates but still lands in spam | Message design |
| Forwarding | Only forwarded copies fail | DKIM, ARC at the forwarder |

## Is your authentication set up and aligned?

This is the first thing to check, and the most common cause for small businesses.

Gmail's [sender guidelines](https://support.google.com/mail/answer/81126) require every sender to "set up SPF or DKIM email authentication for your sending domains", have valid forward and reverse DNS, use TLS, keep spam rates "below 0.3%", and format messages according to RFC 5322. Yahoo's [best practices](https://senders.yahooinc.com/best-practices/) set the same baseline: "Implement SPF or DKIM at a minimum."

Bulk senders need more. Gmail treats anyone who "sends close to 5,000 messages or more to personal Gmail accounts within a 24-hour period" as a bulk sender, permanently ([Google FAQ](https://support.google.com/mail/answer/14229414)). Bulk senders need SPF, DKIM, DMARC and alignment; Outlook.com applies similar rules to domains sending more than 5,000 messages a day and rejects non-compliant mail with [550 5.7.515](https://iblockspam.com/smtp-errors/550-5-7-515). The details are in our [Gmail, Yahoo and Microsoft bulk sender requirements](https://iblockspam.com/blog/gmail-yahoo-microsoft-bulk-sender-requirements), and the [Bulk Sender Requirements Checker](https://iblockspam.com/tools/bulk-sender-checker) shows which of them your domain's DNS already meets.

The trap is alignment. Many newsletter, CRM and invoicing tools pass SPF and DKIM for **their** domain, not yours. DMARC only counts a pass for a domain that matches your From address. Turn on custom-domain DKIM and, where offered, a custom return-path in every service that sends as you.

To check your setup:

1. Run the [Email Health Check](https://iblockspam.com/tools/email-health-check) on your domain for SPF, DKIM, DMARC and MX in one scan.
2. Fix SPF with [what an SPF record is](https://iblockspam.com/blog/what-is-spf) and the [SPF Checker](https://iblockspam.com/tools/spf-checker).
3. Fix DKIM with [what DKIM is](https://iblockspam.com/blog/what-is-dkim) and the [DKIM Checker](https://iblockspam.com/tools/dkim-checker).
4. Publish DMARC, starting at `p=none`; see [what DMARC is](https://iblockspam.com/blog/what-is-dmarc).

A Gmail bounce of [550 5.7.26](https://iblockspam.com/smtp-errors/550-5-7-26) means the message failed authentication outright.

## Is your sender reputation or spam rate the problem?

Receivers learn from how their users react to your mail. Microsoft says many factors influence its filtering, including "the sending IP, domain, email authentication, list accuracy, complaint rates, content", and that "one of the principal factors in driving down a sender's reputation" is the junk email complaint rate ([Microsoft Learn](https://learn.microsoft.com/en-us/defender-office-365/external-senders-mail-flow-troubleshooting)).

The published thresholds:

| Provider | Spam rate guidance |
|---|---|
| Gmail | Keep it "below 0.10%" and avoid ever reaching 0.3% or higher. Bulk senders above 0.3% lose eligibility for mitigation until the rate stays below 0.3% for 7 consecutive days |
| Yahoo | "Keep your spam rate below 0.3%", measured on mail delivered to the inbox |
| Microsoft | No published number; the complaint rate is a principal factor |

Things that raise complaints: mailing people who didn't ask, old or bought lists, no easy unsubscribe, and unexpected frequency. Microsoft recommends double opt-in for newsletters and says bounced addresses "put your outbound email at risk for further scrutiny." Monitor Gmail's rate in Postmaster Tools, and see the [email deliverability checklist](https://iblockspam.com/blog/email-deliverability-checklist) for list hygiene.

One more reputation killer: a compromised mailbox sending spam. If a user suddenly can't send, or you see mail you didn't write, check [signs an email account is compromised](https://iblockspam.com/blog/signs-email-account-compromised) and [Microsoft 365 user blocked from sending](https://iblockspam.com/blog/microsoft-365-user-blocked-from-sending).

## Is your IP or domain on a blocklist?

Blocklist listings more often cause rejections than spam placement, but they belong in any diagnosis. Check your sending IPs with the [Blacklist Checker](https://iblockspam.com/tools/blacklist-checker). It never reports a list it couldn't query as clean: lists that refuse public lookups, such as Spamhaus, show as "not tested" with a link to check directly.

Microsoft runs its own blocked senders list. A bounce of [550 5.7.606-649](https://iblockspam.com/smtp-errors/550-5-7-606-649) means your IP is on it, and Microsoft's delist portal at sender.office.com handles removal. Fix the cause first: Microsoft warns that "the IP address might be blocked again" if the mail is abusive. Our guide to [removing your domain or IP from a blacklist](https://iblockspam.com/blog/remove-domain-ip-from-email-blacklist) covers the major lists.

## Does your sending server have reverse DNS?

If you use Microsoft 365, Google Workspace or a major email service, the provider handles this. If you run your own server, it's on you. Gmail says "the public IP address of a sending SMTP server must have a corresponding PTR record that resolves to a hostname," and Yahoo asks for "valid, meaningful, non-generic reverse DNS (PTR) records." Microsoft says it "might not accept email from senders who fail a reverse-DNS lookup."

Check with the [PTR Lookup](https://iblockspam.com/tools/ptr-lookup) and follow [reverse DNS for mail servers](https://iblockspam.com/blog/reverse-dns-ptr-records-for-mail-servers). Gmail's [550 5.7.25](https://iblockspam.com/smtp-errors/550-5-7-25) error is the giveaway.

## Could your content or links be the cause?

Content matters less than authentication and reputation, but the providers do publish a few rules:

- Google: links in the body "should be visible and easy to understand", "don't use HTML and CSS to hide content", and "don't mix different types of content in the same message."
- Microsoft: links, unsubscribe and profile pages should "all point to the same domain", and avoid messages "composed entirely of an image" or with large images and attachments. The From name and subject should make clear who you are and what the message is about.
- M3AAWG: the domains used "in both email headers and body content are an integral part of a sender's reputation" ([Sender BCP, 2026](https://www.m3aawg.org/sites/default/files/doc_files/m3aawg-sender-best-common-practices-aug-27-2026.pdf)). A link to a domain with a poor reputation can drag a clean message down.

## Are you sending from a new domain or IP?

New senders have no history, and filters treat no history with caution. M3AAWG says the reputation of a newly registered domain "usually starts as unknown, which makes it similar to bad", and recommends starting "low and slow", suggesting six weeks of warm-up as an average. Microsoft says new IPs "typically don't have any reputation" and expects a new IP to be "fully ramped within a couple of weeks or less", depending on volume, list accuracy and complaints. Google says to "start with a low sending volume to engaged users, and slowly increase the volume over time."

If Gmail returns [421 4.7.28](https://iblockspam.com/smtp-errors/421-4-7-28), it's limiting an unusual rate of mail; slow down rather than retry harder.

## Is forwarding breaking your authentication?

If only some recipients see spam placement, and they forward mail from another address to Gmail or Outlook.com, forwarding may be the cause. The forwarding server isn't in your SPF record, so SPF fails; DKIM usually survives. Google says DMARC alignment isn't required for forwarded or mailing list messages, and Yahoo asks forwarders to "implement ARC." Your part is to sign everything with aligned DKIM. See [why forwarding breaks SPF and DMARC](https://iblockspam.com/blog/email-forwarding-breaks-spf-dmarc-arc).

## Why does Outlook or Microsoft 365 put my email in Junk?

Microsoft consumer accounts and business tenants both use Microsoft's filtering, but each business tenant also applies its own policies, allow lists and block lists. Ask a recipient for the headers of a junked message and paste them into the [Email Header Analyzer](https://iblockspam.com/tools/email-header-analyzer). Look at:

- `compauth` in Authentication-Results. Reason `001` means the message "failed implicit authentication": your domain had no records, or only weak ones, such as SPF `~all` or a DMARC policy of `p=none` ([Microsoft Learn](https://learn.microsoft.com/en-us/defender-office-365/message-headers-eop-mdo)).
- `CAT` and `SFV` in `X-Forefront-Antispam-Report`. `CAT:SPM` is spam, `CAT:BULK` is bulk, `CAT:SPOOF` is spoofing. Microsoft now says the `SCL` value "doesn't determine whether the message is identified as spam" in cloud organizations, so read `CAT` instead.

If the verdict is wrong, Microsoft suggests working "with the recipient to submit this false positive message to Microsoft for analysis." A recipient can also add you as a safe sender, as shown in [how to whitelist a sender](https://iblockspam.com/blog/whitelist-sender-microsoft-365-google-workspace). Admins on the receiving side can use [Microsoft 365 emails going to Junk](https://iblockspam.com/blog/microsoft-365-emails-going-to-junk).

## How do I diagnose spam placement step by step?

1. **Send a test** to the [Email Deliverability Test](https://iblockspam.com/tools/deliverability-test) from the exact service that's having trouble.
2. **Scan your domain** with the [Email Health Check](https://iblockspam.com/tools/email-health-check). Fix any missing or failing SPF, DKIM or DMARC.
3. **Check the sending IP** with the [Blacklist Checker](https://iblockspam.com/tools/blacklist-checker) and the [PTR Lookup](https://iblockspam.com/tools/ptr-lookup).
4. **Read any bounce** with the [SMTP error code lookup](https://iblockspam.com/tools/smtp-error-codes).
5. **Get headers from a junked copy** and check SPF, DKIM, DMARC, alignment and the filter verdict.
6. **Look at reputation data**: Google Postmaster Tools for Gmail, and Microsoft's Smart Network Data Services for your IPs.
7. **Fix one thing at a time, then test again.** Reputation recovers over days and weeks, not minutes.

## Next steps

- Run the [Email Deliverability Test](https://iblockspam.com/tools/deliverability-test) now; it takes one email.
- Make sure every service that sends as your domain passes aligned DKIM.
- Work through the [email deliverability checklist](https://iblockspam.com/blog/email-deliverability-checklist) if you send newsletters or bulk mail.
- If your SPF, DKIM or DMARC records might change without you noticing, iBlockSpam [domain monitoring](https://iblockspam.com/features/domain-monitoring) alerts you to drift.

Browse our other guides on [running email day to day](https://iblockspam.com/blog/topic/operations).

## Frequently asked questions

### Why are my emails suddenly going to spam in Gmail?

Look for what changed: a new sending service that isn't in SPF or doesn't sign with your domain, a DNS edit that broke a record, a campaign that drew spam reports, or a compromised account sending spam. Gmail requires SPF or DKIM, reverse DNS, TLS and a spam rate below 0.3% from every sender.

### Why do my emails go to junk in Outlook?

Microsoft weighs the sending IP, domain, authentication, list accuracy, complaint rates and content, and calls the junk complaint rate a principal factor. Mail to business Microsoft 365 users also follows each recipient organization's own policies. Check the recipient's headers for compauth and CAT values to see why.

### Does my spam rate matter if I only send normal business email?

Yes. Gmail asks every sender, not just bulk senders, to keep the spam rate reported in Postmaster Tools below 0.3%, and recommends staying under 0.1%. Yahoo also sets 0.3%. A few complaints from a small audience can push a low-volume sender over those levels quickly.

### Can a brand-new domain cause emails to go to spam?

It can. M3AAWG says a newly registered domain's reputation usually starts as unknown, which filters treat with more scrutiny, and Microsoft says new sending IPs have no reputation in its systems. Send to engaged recipients first and raise volume gradually; M3AAWG suggests six weeks of warm-up as an average.

### How can I test whether my email lands in spam?

Send a real message to a test service, such as our Email Deliverability Test, to see its SPF, DKIM and DMARC results, reverse DNS, blocklist status and a spam verdict. Then send to your own Gmail and Outlook.com accounts and read the headers. No test can predict every receiver's decision.

## Sources

- [Gmail Help: Email sender guidelines](https://support.google.com/mail/answer/81126)
- [Gmail Help: Email sender guidelines FAQ](https://support.google.com/mail/answer/14229414)
- [Yahoo Sender Hub: Sender best practices](https://senders.yahooinc.com/best-practices/)
- [Microsoft Learn: Troubleshooting mail sent to Microsoft 365](https://learn.microsoft.com/en-us/defender-office-365/external-senders-mail-flow-troubleshooting)
- [Microsoft Learn: Anti-spam message headers](https://learn.microsoft.com/en-us/defender-office-365/message-headers-eop-mdo)
- [Microsoft Support: Fix NDR error 550 5.7.515 in Outlook.com](https://support.microsoft.com/en-us/outlook/fix-ndr-error-550-5-7-515-in-outlook-com)
- [M3AAWG Sender Best Common Practices, Version 4.0 (August 2026)](https://www.m3aawg.org/sites/default/files/doc_files/m3aawg-sender-best-common-practices-aug-27-2026.pdf)

## Free tools for this guide

- [Email Deliverability Test](https://iblockspam.com/tools/deliverability-test): Send one email and see its SPF, DKIM and DMARC results, reverse DNS, blocklists, TLS and spam verdict.
- [Bulk Sender Requirements Checker](https://iblockspam.com/tools/bulk-sender-checker): Check your domain against the Gmail, Yahoo and Outlook.com bulk sender rules that DNS can show, with a checklist per provider.
- [Email Health Check](https://iblockspam.com/tools/email-health-check): Grade your domain's MX, SPF, DKIM, DMARC and transport security in one scan.
- [Blacklist Checker](https://iblockspam.com/tools/blacklist-checker): Check an IPv4 or IPv6 address, or your mail servers, against public spam blocklists, with policy and delisting links.

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