What Is Email Spoofing and How Does It Work?
By Srini Seethapathy · September 26, 2025
Email spoofing is a deceptive technique where the sender's identity or address in an email is forged or altered to make it appear as if the message came from a trusted or legitimate source other than the actual sender. This practice is essentially a form of identity fraud, where the attacker pretends to be someone they are not, potentially compromising an organization’s email security. Scammers commonly use email spoofing to hide the true origin of an email message. This in turn increases the chances that the recipient will respond as they hoped.
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Email spoofing motivations
The motivations and uses for email spoofing are diverse, ranging from nuisance to serious criminal activity.
Malicious intentions
- Phishing and Data Theft. Spoofing is a cornerstone of phishing attacks, where the goal is to trick recipients into revealing sensitive information such as login credentials (usernames and passwords), credit card numbers, bank account details, social security numbers, or other personal data. By appearing trustworthy, the spoofed email makes the victim more likely to respond to these requests.
- Malware Distribution. Attackers use spoofed emails to distribute malware, including viruses, spyware, trojans, and ransomware. The deceptive sender increases the likelihood that recipients will open malicious attachments or click dangerous links, thereby infecting their computers or networks.
- Financial Fraud and Funds Theft. A significant motivation is financial gain, often through business email compromise schemes. This involves tricking employees, especially those in finance, into approving fraudulent wire transfers, sending money, making unauthorized purchases, or revealing payment information to the attacker's account. Account takeover (ATO) attacks also fall into this category.
- Hiding Identity and Anonymity. Spoofing allows scammers and malicious users to conceal their true origin and identity, making it harder for them to be discovered, shut down, or prosecuted. This anonymity increases the chances of recipients responding to spam, phishing, or malware-laden emails.
- Bypassing Email Filters. Attackers spoof email addresses to evade spam filters, as emails from seemingly trusted sources are less likely to be flagged as spam and more likely to reach the recipient's inbox.
- Tarnishing Reputation and Spreading Disinformation. Spoofed emails can be used to damage the reputation of the assumed sender or their organization by sending out malicious links, false information, or statements that make them appear compromised or have ill intent. This can also extend to manipulating stock prices or influencing public opinion.
- Personal Damage and Threats. In some cases, the intent is personal, such as gaining access to a target's computer data, business contacts, or social media accounts. Spoofing can be used to send out fake emails appearing to come from the target, corroding the trust of their contacts. It can also be used for harassment, threats, extortion, or blackmail.
- Espionage. Both corporate and state-sponsored actors may use email spoofing to gain access to trade secrets, intellectual property, or sensitive government information.
Legitimate uses
While most often used for malicious intent, spoofing can also be used legitimately. An example might include "authorized” or “on-behalf-of” sending. This involves CRMs and marketing and ticketing systems that legitimately set "From/Reply-to" to the brand domain with proper SPF/DKIM/DMARC alignment (or SRS for forwarded emails). This appears like spoofing but is authenticated and contracted.
How email spoofing works
Email spoofing is possible primarily because the Simple Mail Transfer Protocol (SMTP), the main protocol used for sending emails, does not include a built-in authentication mechanism to verify the sender's identity. The underlying systems of the web were built on implicit trust, focusing more on accurate data transmission than on content security or sender verification.
Here's a breakdown of how email spoofing works:
- Forgery of Email Headers. Attackers use software tools, basic scripts, or even directly connect to an SMTP server to programmatically change specific fields within the email header. These manipulated fields include the "From," "Reply-To," and "Return-Path" addresses. The email client automatically enters the sender address, but outgoing email servers often cannot determine if the sender address is legitimate or spoofed.
- SMTP's Lack of Authentication. When an email is sent via SMTP, the initial connection provides two pieces of address information: "MAIL FROM" (also known as the Return-path header) and "RCPT TO" (the recipient's address). Subsequently, the sending system sends the "DATA" command, which includes header items like "From," "Reply-to," and "Sender". By default, the system does not check if the sender is authorized to send on behalf of these addresses. Consequently, the recipient's email client displays the forged address from the "From:" header, making it appear authentic.
- Separation of Envelope and Header. An email effectively has two parts related to addressing: the header (what the recipient sees) and the SMTP envelope (the information servers use for delivery). Crucially, these two do not have to match for an email to be successfully transmitted. Since the SMTP envelope typically doesn't check the header, and recipients usually don't scrutinize the technical details in the full email header, spoofing becomes relatively easy.
- Exploiting Open Relays. Some mail servers, especially older or misconfigured ones, act as "open relay servers." These servers allow anyone with the necessary knowledge to connect and send messages that appear to be from any address of their choice, whether valid or fictitious. Even if a mail server uses an SMTP service extension for authentication, it doesn't prevent authenticated users (e.g., those with compromised accounts) from sending spoofed emails.
- Bolstering Credibility. To make spoofed emails more convincing, attackers may copy a legitimate company's logo, branded art, and other design elements. They might also use messages and language that seem relevant to the imitated entity. While the full email header does log the IP addresses of the servers an email traverses, revealing its true route and sender, many users do not inspect these headers.
How to spot email spoofing
Email spoofing can be detected by carefully scrutinizing various elements of an email, from its technical headers to its visible content and sender information.
- Check the Email Header for Discrepancies.
- "From," "Reply-To," and "Return-Path" Fields. Attackers programmatically change these specific fields within the email header to make the message appear from a different source. While recipients usually see the "From" header, the "MAIL FROM" (Return-path) used for delivery is generally not visible to the end-user, and by default, no checks are done to ensure the sending system is authorized for that address.
- "Received" Section. The full email header logs the IP addresses of the servers an email traverses. By inspecting the "Received" lines, you can identify the true route and sender. If a different domain appears here than the one in the "From" address, the email is likely forged.
- "Received-SPF" Status. Sender Policy Framework (SPF) records list authorized servers to send emails for a domain. If an email comes from an unauthorized server, the "Received-SPF" field will display a "Fail" or "Softfail" status, indicating a potential spoof.
- Look for Disconnects in Sender Information.
- Display Name vs. Email Address. A common sign of a spoofed email is when the displayed sender name does not match the actual email address, especially if the domain in the email address looks suspicious. For instance, a display name like "Amazon Support" but an email ending with a different domain, or a misspelled domain (e.g., quick0rders.com instead of quickorders.com), is highly suspicious.
- Inconsistencies in Signatures. Check if information in the email signature, like a telephone number, doesn't align with what is known about the purported sender.
- Assess the Email Content and Tone.
- Sense of Urgency or Threatening Language. Spoofed emails often use alarming, aggressive, or urgent messaging to provoke immediate action without critical thought.
- Requests for Personal Information. Be wary of emails asking for sensitive data such as account credentials, credit card numbers, or social security numbers. Companies generally do not ask for usernames or passwords via email.
- Unsolicited Links or Attachments. Avoid clicking links or downloading attachments from suspicious or unknown senders. Spoofed emails are often used to deliver malware or direct users to malicious websites.
- Poor Spelling and Grammar. Professional organizations typically send well-crafted emails. Numerous errors in spelling or grammar can be a red flag.
- Generic Greetings. Spoofed emails may use vague salutations like "Dear Customer" instead of your specific name.
- Copy and Paste Content into a Search Engine. Text used in common phishing attacks may already be reported and published online.
- Verify Through Alternative Channels. If an email seems suspicious, always use another method of communication to contact the supposed sender, such as calling them via phone, using interoffice chat, or visiting their official website to verify the request. Do not use contact information provided in the suspicious email itself.
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How to defend against email spoofing
Use email security protocols and filters to protect your organization against email spoofing.
- SPF, DKIM, and DMARC. These protocols work together to authenticate emails and detect forged sender addresses. Email filters check these protocols. If an email fails DMARC checks, organizations can configure policies to label, reject, quarantine, or allow it through. Google now requires SPF/DKIM on all incoming messages to Gmail accounts, and other providers are likely to follow suit.
- Antimalware Software. Antimalware solutions can detect and block spoofed emails before they reach your inbox by identifying suspicious senders or websites.
- Email Filters. Simple email filters can limit the number of suspicious emails that get through.
- Secure Email Gateway. These systems filter suspicious messages and block emails from known spoofed addresses at the network level, before they impact users.
Trellix Email Security delivers comprehensive protection for inbound and outbound emails, safeguarding your organization. With advanced threat detection, actionable alerts, and email claw-back capabilities, you can reduce attacks using AI, machine learning, and analytics.
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Email spoofing FAQ
Email spoofing is a deceptive tactic where the sender's identity is faked to appear legitimate, often to hide the true origin and prompt a desired response from the recipient.
Email spoofing can be motivated by a range of intentions, from minor nuisances to serious criminal activities. These include:
- Phishing and data theft
- Malware distribution
- Financial fraud and fund theft
- Hiding identity and gaining anonymity
- Bypassing email filters
- Tarnishing reputation and spreading disinformation
- Personal damage and threats
- Espionage
You can detect email spoofing by carefully examining various elements of an email:
- Check headers for discrepancies in "From," "Reply-To," and "Return-Path" fields, inspecting "Received" IP addresses, and noting "Received-SPF" status (Fail/Softfail)
- Look for sender information disconnects like mismatched display names/email addresses or inconsistent signatures
- Assess content for urgency, requests for personal info, unsolicited links/attachments, poor grammar, and generic greetings
- Verify suspicious emails via alternative, known channels, never using contact info from the suspicious email itself
Several measures can help detect and block spoofed emails:
- SPF, DKIM, and DMARC: These email authentication protocols help detect forged sender addresses. Email filters utilize these, allowing organizations to set policies for labeling, rejecting, quarantining, or permitting emails based on DMARC checks.
- Antimalware Software: These solutions are designed to detect and block spoofed emails by identifying suspicious senders or websites.
- Email Filters: Basic filters can effectively reduce the number of suspicious emails that reach user inboxes.
- Secure Email Gateway: These systems operate at the network level to filter suspicious messages and block emails from known spoofed addresses before they affect users.
Email spoofing resources
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