Simple Mail Transfer Protocol (SMTP) is the standard method that mail servers use to send emails. Organizations typically use an SMTP relay service to send mass emails, such as marketing materials. Some organizations use Gmail as an SMTP relay service, but unfortunately, cybercriminals have found a vulnerability in the Gmail service.

Using this vulnerability, cybercriminals can spoof any organization that also uses Gmail as a relay service. For example, let’s say that a legitimate organization owns the domain sign-doc[dot]com and uses Gmail to relay its marketing emails. Cybercriminals could send phishing emails from a malicious domain, such as wishyoudidntclickthis[dot]com, and disguise the emails by spoofing the legitimate domain, sign-doc[dot]com. Since the spoofed domain is being relayed through Gmail, most email clients will consider the malicious email safe and allow it to pass through security filters.

Follow the tips below to stay safe from similar scams:

  • This type of attack isn’t limited to Gmail. Other SMTP relay services could have similar vulnerabilities. Even if an email seems to come from a legitimate sender, remain cautious.
  • Never click on a link or download an attachment in an email that you were not expecting.
  • If you need to verify that an email is legitimate, try reaching out to the sender directly through phone call or text message.