# What is Spam Email and How to Prevent It?

> Spam email is unsolicited bulk mail. Learn how filters score it, what authentication records block it at the source, and how to protect your domain.

**Spam email is any unsolicited message sent in bulk to recipients who did not ask for it — ranging from harmless advertisements to malicious links that steal credentials or install malware.**

![What is Spam Email and How to Prevent It?](/images/generated/what-is-spam-email-and-how-to-prevent-it.webp)

According to Kaspersky's 2025 spam and phishing report, roughly 45% of all global email traffic in 2025 was classified as spam — close to one in every two messages sent. While modern filters catch the vast majority before it reaches an inbox, the volume is large enough that even a small miss rate exposes users to thousands of unwanted or dangerous messages each year.

## Common spam techniques

Spammers rely on social-engineering to make messages feel urgent or credible. Recognizing the patterns is the first line of defense:

![Checklist of five common spam tactics, including fake money schemes, fake discounts, and urgent requests.](/images/figures/what-is-spam-email-and-how-to-prevent-it-fig1.webp)
*Typical social-engineering tactics spammers use to make messages look legitimate.*

- **"Make money fast" schemes** promising quick riches with minimal effort.
- **Fake discounts** on popular products or services with countdown timers.
- **Investment offers** for unknown companies or "guaranteed" crypto returns.
- **Advance-fee scams** that ask for a small payment to unlock a larger reward.
- **Urgent requests** that pressure the recipient to act before they can think.
- **Lookalike sender addresses** that imitate a trusted brand or colleague.

## Types of spam email

Not all spam is the same. Understanding the categories helps you recognize them faster:

- **Commercial spam:** Unsolicited advertising for real (but unwanted) products.
- **Malspam:** Spam carrying malware — infected attachments or drive-by-download links. See [how malspam works and how to stop it](/learning/how-does-malspam-work-and-how-to-stop-it) for a deeper look.
- **Phishing:** Targeted messages that impersonate trusted entities to steal credentials or financial data. Learn the full attack pattern in [what is phishing](/learning/what-is-phishing).
- **Spoofing spam:** Messages that forge the From address to appear as a legitimate domain — the attack that email authentication is designed to block.
- **Health and financial spam:** Ads for supplements, miracle cures, debt relief, and loan offers.
- **Adult content spam:** Unsolicited pornographic or adult product advertisements.

## How spam filters score your mail

Every major mailbox provider — Gmail, Microsoft 365, and others — runs inbound messages through a multi-signal scoring engine before delivery. Understanding what triggers that engine helps both senders and recipients.

**Content signals:** Filters analyze subject lines, body text, HTML structure, and image-to-text ratios. Classic red flags include excessive capitalization, "FREE" in the subject, hidden text, and single-image bodies with no real text.

**Sender reputation:** The IP address and domain sending the mail carry a reputation score based on past behavior. High bounce rates, spam complaints, and appearances on blocklists all lower this score. You can check whether your sending infrastructure has ended up on a blocklist with the [blocklist checker](/tools/blocklist-checker).

**Engagement history:** Gmail and Microsoft 365 track whether recipients open, reply to, or delete without opening messages from a given sender. Low engagement signals spam even when content looks clean.

**Authentication pass/fail:** Filters give a significant reputation boost to mail that passes SPF, DKIM, and DMARC, and may apply extra scrutiny — or route directly to spam — when authentication fails. This is the signal you control most directly.

## Sender-side defenses: authentication

Authentication is the most effective tool a domain owner has against spam and spoofing. Three DNS records work together:

![Authentication records that reduce spam and spoofing](/images/figures/what-is-spam-email-and-how-to-prevent-it-fig2.webp)
*SPF, DKIM, and DMARC work together to prove a message is legitimate and hasn't been tampered with.*

**[SPF (Sender Policy Framework)](/learning/what-is-spf)** publishes a list of IP addresses and services authorized to send email for your domain. When a receiving server checks the SPF record and finds the sending IP listed, it passes that check. Generate a correct SPF record with the [SPF generator](/tools/spf-generator) and verify your current record with the [SPF checker](/tools/spf).

**[DKIM (DomainKeys Identified Mail)](/learning/what-is-dkim)** adds a cryptographic signature to every outgoing message. Recipients verify the signature against your public key in DNS, confirming the message wasn't altered in transit. Check your DKIM configuration with the [DKIM checker](/tools/dkim).

**[DMARC](/learning/what-is-dmarc)** ties SPF and DKIM together and tells receiving servers what to do when mail fails both — quarantine it or reject it outright. Without DMARC, an attacker can forge your From address and SPF/DKIM failures go unaddressed. Build a DMARC record with the [DMARC generator](/tools/dmarc-generator).

Together, these three records are the primary reason spoofed spam from your domain lands in spam folders (or is rejected before delivery) rather than reaching your recipients' inboxes. For a concise overview of all three protocols in one place, see [what are DMARC, DKIM, and SPF](/resources-post/what-are-dmarc-dkim-and-spf).

## Recipient-side defenses: inbox hygiene

Authentication protects your domain's sending reputation. Inbox hygiene protects you from spam sent by others:

- **Separate business and personal addresses.** Mixing them exposes your work address to consumer data brokers and marketing lists.
- **Enable and tune spam filters.** Gmail and Microsoft 365 both allow users to report messages as spam, which trains the filter for your account. Review your spam/junk folder occasionally to rescue false positives.
- **Think before you click.** Hover over links to preview the destination URL. Avoid clicking "unsubscribe" links in messages you didn't sign up for — these can confirm your address is active.
- **Confirm urgent requests out of band.** If an email asks for money or sensitive data, call the sender directly using a number you already know.
- **Inspect the full email header.** Mismatches between the From address, Reply-To address, and sending server are a reliable sign of a spoofed or forged message. Use the [email header analyzer](/tools/email-header-analyzer) to decode headers without reading raw DNS output.
- **Check your domain's overall security posture.** The [Email Security Score](/tools/email-security-score) audits your SPF, DKIM, and DMARC records in one pass and flags gaps attackers could exploit.
- **Monitor for blocklist appearances.** A domain that ends up on a blocklist sees its legitimate mail treated as spam by recipient servers. Regular checks with the [domain reputation checker](/tools/domain-reputation) help you catch problems early.

## Quick takeaways

- Roughly 45% of global email traffic is spam (Kaspersky, 2025).
- Spam ranges from harmless ads to credential-stealing phishing and malware delivery.
- Filters score mail on content, sender reputation, engagement history, and authentication.
- SPF, DKIM, and DMARC are the sender-side controls that matter most.
- Inbox hygiene — separate addresses, trained filters, header inspection — covers the recipient side.
- Deploy authentication records and verify them; use the [Email Security Score](/tools/email-security-score) to audit your setup.

## Frequently asked questions

### What is the difference between spam and phishing?

Spam is unsolicited bulk mail — often harmless advertising, though it may carry malware. Phishing is a targeted attack that impersonates a trusted entity (a bank, a colleague, a known SaaS vendor) to trick the recipient into surrendering credentials or transferring money. All phishing arrives via email, but not all spam is phishing. See [what is phishing](/learning/what-is-phishing) for a full breakdown of attack patterns.

### How does SPF help stop spam?

SPF lets domain owners publish a list of authorized sending servers in DNS. When a receiving mail server checks this record and finds the sending IP is not on the list, it can treat the message as suspicious or reject it outright. This makes it harder for attackers to forge your domain in spam campaigns, because the forged message will fail SPF at the recipient's server.

### What role does DKIM play in email security?

DKIM adds a cryptographic signature to every outgoing message, tied to your domain. Recipients verify that signature against your public DNS key. If the message was altered in transit — or if the signature is missing — the DKIM check fails. Passing DKIM is also required for DMARC alignment, which is what gives domain owners control over what happens to unauthenticated mail.

### Why should I implement DMARC?

SPF and DKIM each cover one authentication signal. DMARC ties them together and adds policy enforcement: you tell receiving servers to quarantine or reject mail that fails both checks. Without DMARC, even a domain with perfect SPF and DKIM records has no way to instruct recipients to reject spoofed messages. DMARC also unlocks aggregate reporting, which shows you every source sending mail as your domain — legitimate or not.

### Can spam filters block legitimate mail by mistake?

Yes — this is called a false positive. Poorly formatted HTML, certain trigger phrases, or a domain that recently appeared on a blocklist can cause legitimate messages to be quarantined. If your organization's outbound mail is ending up in spam folders, start by auditing authentication records with the [Email Security Score](/tools/email-security-score), then check whether your sending IP or domain has been listed using the [blocklist checker](/tools/blocklist-checker). For a deeper look at filtering behavior, see [what is email filtering software](/learning/what-is-email-filtering-software-services-prevent-spam).