Which tool is used to analyze email headers during an investigation of an email security incident?

The analysis of email headers is essential in investigating email security incidents because it reveals critical information about the origin and route of an email message. This can include details such as the sending IP address, the servers through which the email passed, timestamps, and any potential indicators of spoofing or forgery.

The tool ipTRACKERonline.com is designed specifically for tracking IP addresses and analyzing email headers, making it particularly useful in cybersecurity investigations. By entering an email header into ipTRACKERonline, an investigator can extract the path the email took, identify the sender's location, and gain insights into whether the email came from a legitimate source or was compromised.

Other tools mentioned, while useful in various contexts, do not focus specifically on the analysis of email headers related to security incidents. MailTester.com is primarily for checking the deliverability of emails by analyzing how a server responds, Google Safe Browsing is aimed at checking URLs against a database of known threats, and SenderScore provides metrics on email sender reputation but does not analyze headers directly. Therefore, ipTRACKERonline.com is the most appropriate choice for this task.