What are Spam Emails? Causes, Risks and Prevention

Spam is unsolicited, bulk email sent to large numbers of recipients — usually to advertise, to phish for credentials, or to spread malware. Also called junk mail, it clogs inboxes, wastes resources, and carries real security risk. There are two sides to defending against it: keeping spam out of your inbox as a recipient, and stopping spammers from using your domain to send it. Both come down to email authentication — SPF, DKIM, and DMARC — and good filtering.

How spam works

Spam runs on volume and deception. A typical campaign follows the same path:

• Harvesting targets. Spammers scrape addresses from websites, buy lists, or pull them from data breaches, often using bots to gather millions at a time.
• Crafting the message. The content is built to entice or alarm — fake offers, urgent account warnings, or a trusted brand impersonated through spoofing.
• Sending at scale. Messages go out through botnets, compromised accounts, or misconfigured mail servers acting as open relays, frequently forging a legitimate domain in the From: address.
• Evading filters. Attackers rotate sending IPs, vary the text, and exploit domains that lack SPF or DKIM, because unauthenticated mail is easier to disguise.
• Getting a click. A single recipient who opens an attachment or clicks a link can hand over credentials, trigger a malware install, or start a fraudulent payment.

For example, a spam message might impersonate a bank and push the reader to a fake login page that captures their password.

Why spam is a problem

• Security risk. Spam is the delivery vehicle for most phishing and malware, putting personal and company data at risk.
• Resource drain. High volumes load down mail servers and filters and raise bandwidth and support costs.
• Lost productivity and trust. Junk clutters inboxes and erodes confidence in email as a channel.
• Reputation damage. If spammers spoof your domain, your brand takes the blame — and your legitimate mail can start landing in spam folders too.

How to stop and avoid spam in your inbox

As a recipient, you cannot stop spam being sent, but you can keep most of it away from you:

• Report, don't just delete. Marking messages as spam trains your provider's filter and improves accuracy for everyone.
• Never engage. Don't reply, click links, or use "unsubscribe" on clearly malicious mail — it confirms your address is live.
• Guard your address. Avoid posting it publicly; use aliases or a separate address for signups so you can cut off a leaked one.
• Keep filters on. Leave your provider's spam filtering enabled; it scores content, sender reputation, and authentication results automatically.
• Verify before trusting. When a message looks off, check the email header — a dmarc=fail result is a strong sign of a spoofed sender.

How domain owners prevent their domain being used for spam

If you own a domain, publishing authentication records stops spammers from forging your name — which protects your recipients and your reputation at once:

• SPF lists the servers allowed to send as your domain, so forgeries from anywhere else can be rejected. Verify yours with the SPF lookup tool.
• DKIM signs your mail cryptographically, so tampering and impersonation are detectable.
• DMARC ties SPF and DKIM to your visible From: domain and, at p=reject, tells receivers to refuse mail that fails — the setting that actually blocks spoofed spam. Read your DMARC reports to see who is sending as you before you enforce.
• Harden your servers. Require authentication so your MTA can't be abused as an open relay, enforce TLS with MTA-STS, and publish a PTR record so your sending IP resolves cleanly.

This side also keeps you compliant: since February 2024, Gmail and Yahoo require bulk senders (more than 5,000 messages a day) to authenticate with SPF, DKIM, and DMARC and to keep their spam-complaint rate under 0.3%. Check every record at once with the Email Security Score.

Related reading

• What are DMARC, DKIM, and SPF?
• What is email filtering and how does it prevent spam?
• What is phishing?