To determine whether the connection was successful after a user clicked on a link in a phishing email, the most relevant log source to analyze would be the network logs. These logs would provide information on outbound and inbound traffic, allowing the analyst to see if the user's system connected to the remote server specified in the phishing link. Network logs can include details such as IP addresses, domains accessed, and the success or failure of connections, which are crucial for understanding the impact of the phishing attempt.
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CompTIA Security+ SY0-701 Course Content: Domain 04 Security Operations.
CompTIA Security+ SY0-601 Study Guide: Chapter on Incident Response.