The SMTP Open Relay Test Tool is a simple web application that allows users to test whether an SMTP server is configured as an open relay. An open relay is an SMTP server that forwards email messages from anyone on the internet to any email address, without requiring any authentication. Open relays are considered insecure and can be exploited by spammers to send large volumes of unsolicited email (spam).

1. User Interface: The tool has a user-friendly web interface where users can input the domain they want to test.

2. MX Record Lookup: The application starts by looking up the Mail Exchange (MX) records for the provided domain using the dns.resolver library. MX records specify the mail servers responsible for receiving emails for the domain.

3. SMTP Connection Testing: The tool then attempts to connect to each mail server identified in the MX records. It uses the smtplib library to establish SMTP connections.

4. SMTP Test Email: Once the connection is established, the tool sends a test email to itself (using a predefined email address, e.g., geek@gmail.com) through the SMTP server. The email contains a simple subject and body, indicating that it is a test email.

5. Open Relay Detection: If the SMTP server accepts the test email and successfully forwards it without requiring authentication, it is considered an open relay. Otherwise, if the server rejects the email or requires authentication, it is not an open relay.

6. SPF Record Test: Additionally, the tool queries the SPF (Sender Policy Framework) record for each domain using dns.resolver.resolve(). SPF is a DNS TXT record that specifies the authorized mail servers for a domain. It checks if the SPF record exists and whether the sender email is authorized to send emails on behalf of the domain.

7. Results Display: The application displays the results in a tabular format on the web page. It shows the MX records, whether the SMTP server is an open relay or not, and the SPF records along with SPF check results.