Email spoofing is the creation of email messages with a forged sender address.[1] The term applies to email purporting to be from an address which is not actually the sender's; mail sent in reply to that address may bounce or be delivered to an unrelated party whose identity has been faked. Disposable email address or "masked" email is a different topic, providing a masked email address that is not the user's normal address, which is not disclosed (for example, so that it cannot be harvested), but forwards mail sent to it to the user's real address.[2]

The original transmission protocols used for email do not have built-in authentication methods: this deficiency allows spam and phishing emails to use spoofing in order to mislead the recipient. More recent countermeasures have made such spoofing from internet sources more difficult but they have not eliminated it completely; few internal networks have defences against a spoof email from a colleague's compromised computer on that network. Individuals and businesses deceived by spoof emails may suffer significant financial losses; in particular, spoofed emails are often used to infect computers with ransomware.

Technical details

When a Simple Mail Transfer Protocol (SMTP) email is sent, the initial connection provides two pieces of address information:

Together, these are sometimes referred to as the "envelope" addressing – an analogy to a traditional paper envelope.[3] Unless the receiving mail server signals that it has problems with either of these items, the sending system sends the "DATA" command, and typically sends several header items, including:

The result is that the email recipient sees the email as having come from the address in the From: header. They may sometimes be able to find the MAIL FROM address, and if they reply to the email, it will go to either the address presented in the From: or Reply-to: header, but none of these addresses are typically reliable,[4] so automated bounce messages may generate backscatter.

Although email spoofing is effective in forging the email address, the IP address of the computer sending the mail can generally be identified from the "Received:" lines in the email header.[5] In malicious cases, however, this is likely to be the computer of an innocent third party infected by malware that is sending the email without the owner's knowledge.

Malicious use of spoofing

Phishing and business email compromise scams generally involve an element of email spoofing.

Email spoofing has been responsible for public incidents with serious business and financial consequences. This was the case in an October 2013 email to a news agency which was spoofed to look as if it was from the Swedish company Fingerprint Cards. The email stated that Samsung offered to purchase the company. The news spread and the stock exchange rate surged by 50%.[6]

Malware such as Klez and Sober among many more modern examples often search for email addresses within the computer they have infected, and they use those addresses both as targets for email, and also to create credible forged From fields in the emails that they send.[citation needed] This is to ensure that the emails are more likely to be opened. For example:

  1. Alice is sent an infected email which she opens, running the worm code.
  2. The worm code searches Alice's email address book and finds the addresses of Bob and Charlie.
  3. From Alice's computer, the worm sends an infected email to Bob, but is forged to appear as if it was sent by Charlie.

In this case, even if Bob's system detects the incoming mail as containing malware, he sees the source as being Charlie, even though it really came from Alice's computer. Meanwhile, Alice may remain unaware that her computer has been infected, and Charlie does not know anything about it at all, unless he receives an error message from Bob.

The effect on mail servers

Traditionally, mail servers could accept a mail item, then later send a Non-Delivery Report or "bounce" message if it could not be delivered or had been quarantined for any reason. These would be sent to the "MAIL FROM:" a.k.a. "Return Path" address. With the massive rise in forged addresses, best practice is now to not generate NDRs for detected spam, viruses etc.[7] but to reject the email during the SMTP transaction. When mail administrators fail to take this approach, their systems are guilty of sending "backscatter" emails to innocent parties – in itself a form of spam – or being used to perform "Joe job" attacks.


The SSL/TLS system used to encrypt server-to-server email traffic can also be used to enforce authentication, but in practice it is seldom used,[8] and a range of other potential solutions have also failed to gain traction.

A number of defensive systems have come into wide use, including:

To effectively stop forged email being delivered, the sending domains, their mail servers, and the receiving system all need to be configured correctly for these higher standards of authentication. Although their use is increasing, estimates vary widely as to what percentage of emails have no form of domain authentication: from 8.6%[10] to "almost half".[11][12][13] For this reason, receiving mail systems typically have a range of settings to configure how they treat poorly-configured domains or email.[14][15]

While there has been research into improving email security, little emphasis has been placed on informing users whose email addresses have been used for spoofing. Currently, only the email recipient can identify a fake email, and users whose addresses are spoofed remain unaware unless the recipient manually scrutinizes the message.[citation needed]

Business email

Business email compromise attacks are a class of cyber crime which use email fraud to attack organizations. Examples include invoice scams and spear-phishing attacks which are designed to gather data for other criminal activities. A business deceived by an email spoof can suffer additional financial, business continuity and reputational damage. Fake emails can also be used to spread malware.

Typically, an attack targets specific employee roles within an organization by sending spoof emails which fraudulently represent a senior colleague, trusted customer, or supplier.[16] (This type of attack is known as spear phishing). The email will issue instructions, such as approving payments or releasing client data. The emails often use social engineering to trick the victim into making money transfers to the bank account of the fraudster.[17]

The United States' Federal Bureau of Investigation recorded $26 billion of US and international losses associated with BEC attacks between June 2016 and July 2019.[18] More recent figures estimate losses of over $50 billion from 2013 to 2022.[19]


See also


  1. ^ Varshney, Gaurav; Misra, Manoj; Atrey, Pradeep K. (2016-10-26). "A survey and classification of web phishing detection schemes: Phishing is a fraudulent act that is used to deceive users". Security and Communication Networks. 9 (18): 6266–6284. doi:10.1002/sec.1674.
  2. ^ Yee, Alaina (6 June 2022). "What is masked email? This new spin on an old practice supercharges your security". PCWorld.
  3. ^ Siebenmann, Chris. "A quick overview of SMTP". University of Toronto. Archived from the original on 2019-04-03. Retrieved 2019-04-08.
  4. ^ Barnes, Bill (2002-03-12). "E-Mail Impersonators". Slate. Archived from the original on 2019-04-13. Retrieved 2019-04-08.
  5. ^ "e-mail impersonators: identifying "spoofed" e-mail". Archived from the original on 2017-06-21. Retrieved 2019-04-08.
  6. ^ Mundy, Simon (11 October 2013). "Fraudsters' fingerprints on fake Samsung deal". Financial Times. Archived from the original on 2019-02-10. Retrieved 2019-04-08.
  7. ^ See RFC3834
  8. ^ "Transport Layer Security for Inbound Mail". Google Postini Services. Archived from the original on 2016-11-11. Retrieved 2019-04-08.
  9. ^ Carranza, Pablo (16 July 2013). "How To use an SPF Record to Prevent Spoofing & Improve E-mail Reliability". DigitalOcean. Archived from the original on 20 April 2015. Retrieved 23 September 2019. A carefully tailored SPF record will reduce the likelihood of your domain name getting fraudulently spoofed and keep your messages from getting flagged as spam before they reach your recipients. Email spoofing is the creation of email messages with a forged sender address; something that is simple to do because many mail servers do not perform authentication. Spam and phishing emails typically use such spoofing to mislead the recipient about the origin of the message.
  10. ^ Bursztein, Elie; Eranti, Vijay (2013-12-06). "Internet-wide efforts to fight email phishing are working". Google Security Blog. Archived from the original on 2019-04-04. Retrieved 2019-04-08.
  11. ^ Eggert, Lars. "SPF Deployment Trends". Archived from the original on 2016-04-02. Retrieved 2019-04-08.
  12. ^ Eggert, Lars. "DKIM Deployment Trends". Archived from the original on 2018-08-22. Retrieved 2019-04-08.
  13. ^ "In First Year, DMARC Protects 60 Percent of Global Consumer Mailboxes". 2013-02-06. Archived from the original on 2018-09-20. Retrieved 2019-04-08.
  14. ^ "Prevent spoofed messages with spoofed senders detection". Archived from the original on 2019-03-23. Retrieved 2019-04-08.
  15. ^ "Anti-spoofing protection in Office 365". Archived from the original on 2019-04-09. Retrieved 2019-04-08.
  16. ^ Joan Goodchild (20 June 2018). "How to Recognize a Business Email Compromise Attack". Security Intelligence. Archived from the original on 23 March 2019. Retrieved 11 March 2019.
  17. ^ "Tips to Avoid Phishing Attacks and Social Engineering". Archived from the original on 2020-12-02. Retrieved 2020-11-17.
  18. ^ "Business Email Compromise Is Extremely Costly And Increasingly Preventable". Forbes Media. 15 April 2020. Archived from the original on 23 October 2021. Retrieved 2 December 2020.
  19. ^ "Business Email Compromise: The $50 Billion Scam".
  20. ^ "Dublin Zoo lost €500k after falling victim to cyber-scam". 22 December 2017. Archived from the original on 8 August 2019. Retrieved 23 October 2021.
  21. ^ "Austria's FACC, hit by cyber fraud, fires CEO". Reuters. 26 May 2016. Archived from the original on 21 March 2021. Retrieved 20 December 2018.
  22. ^ "Te Wananga o Aotearoa caught up in $120k financial scam". NZ Herald. Archived from the original on 20 December 2018. Retrieved 20 December 2018.
  23. ^ "Fire Service scammed out of $52,000". RNZ News. 23 December 2015. Archived from the original on 20 December 2018. Retrieved 20 December 2018.
  24. ^ Hackett, Robert (August 10, 2015). "Fraudsters duped this company into handing over $40 million". Fortune magazine. Archived from the original on 20 December 2018. Retrieved 20 December 2018.
  25. ^ Wallack, Todd (13 December 2018). "Hackers fooled Save the Children into sending $1 million to a phony account". The Boston Globe. Archived from the original on 20 December 2018. Retrieved 20 December 2018.
  26. ^ Australian Competition and Consumer Commission
  27. ^ Powell, Dominic (27 November 2018). "Business loses $300,000 to 'spoofed' email scam: How to protect yourself from being impersonated". Smart Company. Archived from the original on 27 November 2018. Retrieved 14 December 2018.
  28. ^ "Sentence in BEC Scheme". Federal Bureau of Investigation. Archived from the original on 2020-01-31. Retrieved 2020-02-01.