1. Banner Grabbing
   1. A technique used to gain information about servers and take inventory of systems and services.
   2. Can be used legitimately by network administrators or illegitimately by attackers to grab information such as HTTP headers.
2. Banner Grabbing Tools
   1. Netcat
   2. Telnet
   3. Metasploit Framework (MSF)
3. SMTP Enumeration
   1. Important enumeration SMTP fields include:
      1. VRFY
      2. EXPN
      3. RCPT TO
   2. For a list of SMTP header fields, visit this URL:
      1. https://tools.ietf.org/html/rfc4021