Identify mail server
There are several ways to identify a mail server:
- MX Record Lookup: An MX record (Mail Exchanger) is a DNS record that specifies the mail server responsible for accepting email messages on behalf of a domain. You can use a tool like dig or nslookup to look up the MX record for a domain and identify the mail server.
Example: dig mx example.com
- SMTP Banner: When you connect to a mail server using SMTP (Simple Mail Transfer Protocol), the server responds with a banner that includes information about the server, including its name and version. You can use a tool like telnet to connect to the mail server and retrieve the banner.
Example: telnet mail.example.com 25
- VRFY Command: The VRFY (Verify) command is used to verify the existence of a user on a mail server. When you send a VRFY command to a mail server, it responds with a message indicating whether the user exists or not. You can use a tool like telnet to connect to the mail server and send a VRFY command.
Example: telnet mail.example.com 25
followed by VRFY [email protected]
- Banner Grabbing: Banner grabbing is a technique used to retrieve the banner of a mail server by connecting to it using a tool like telnet and sending a command like
HELO
orEHLO
. The server responds with a banner that includes information about the server, including its name and version.
Example: telnet mail.example.com 25
followed by HELO
- Passive DNS: Passive DNS (pDNS) is a technique used to retrieve DNS records from a DNS server without actively querying it. You can use a tool like Shodan or Censys to search for mail servers and retrieve their DNS records.
Example: shodan search "mail server"
or censys search "mail server"
- Network Scanning: Network scanning is a technique used to scan a network for open ports and services. You can use a tool like Nmap to scan a network for open mail ports and identify mail servers.
Example: nmap -p 25,587 example.com
- Whois Lookup: Whois lookup is a technique used to retrieve information about a domain or IP address. You can use a tool like whois to look up the owner of a domain and identify the mail server.
Example: whois example.com
Note: Some of these methods may require permission from the mail server administrator or may be blocked by firewalls or other security measures.