Email spoofing is the creation of email messages with a forged sender address. 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. 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 not eliminated it; few internal networks have defenses 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: MAIL FROM: - generally presented to the recipient as the Return-path: header but not normally visible to the end user, and by default no checks are done that the sending system is authorized to send on behalf of that address. RCPT TO: - specifies which email address the email is delivered to, is not normally visible to the end user but may be present in the headers as part of the "Received:" header. Together, these are sometimes referred to as the "envelope" addressing – an analogy to a traditional paper envelope. 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: From: Joe Q Doe <joeqdoe@example.com> - the address visible to the recipient; but again, by default no checks are done that the sending system is authorized to send on behalf of that address. Reply-to: Jane Roe <Jane.Roe@example.mil> - similarly not checked and sometimes: Sender: Jin Jo <jin.jo@example.jp> - also not checked 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