Certified Ethical Hacker (CEH) v13 312-50v13 — Question 211

As a certified ethical hacker, you are tasked with gaining information about an enterprise's internal network. You are permitted to test the network's security using enumeration techniques. You successfully obtain a list of usernames using email IDs and execute a DNS Zone Transfer. Which enumeration technique would be most effective for your next move given that you have identified open TCP ports 25 (SMTP) and 139 (NetBIOS Session Service)?