How to check on servers that are sending mails

There are several ways to check on servers that are sending emails:

1. Check the server logs: Most email servers have logs that record information about incoming and outgoing emails. You can check these logs to see which servers are sending emails to your server.
2. Use a mail server monitoring tool: There are several tools available that can monitor your email server and provide information about incoming and outgoing emails, including the IP addresses of the sending servers. Some popular options include:
   • MailScanner: A free, open-source email scanner that can monitor your email server and provide information about incoming and outgoing emails.
   • SpamAssassin: A popular open-source spam filtering tool that can also monitor your email server and provide information about incoming and outgoing emails.
   • Postfix: A popular open-source email server that includes a built-in logging mechanism that can be used to monitor incoming and outgoing emails.
3. Use a network monitoring tool: Network monitoring tools can provide information about the IP addresses and ports used by email servers that are sending emails to your server. Some popular options include:
   • Wireshark: A free, open-source network protocol analyzer that can capture and analyze network traffic.
   • Tcpdump: A free, open-source network protocol analyzer that can capture and analyze network traffic.
   • Nagios: A popular open-source network monitoring tool that can monitor network traffic and provide information about incoming and outgoing emails.
4. Check the DNS records: You can check the DNS records of the sending servers to see if they are legitimate or if they are spoofing your domain. You can use tools like dig or nslookup to check the DNS records.
5. Check the email headers: You can check the email headers to see if they contain any information about the sending server, such as the IP address or the domain name. You can use tools like Mailvelope or Email Header Analyzer to check the email headers.
6. Use a mail server debugging tool: Mail server debugging tools can help you troubleshoot issues with your email server and provide information about incoming and outgoing emails. Some popular options include:
   • Telnet: A command-line tool that can be used to connect to your email server and send test emails.
   • Swaks: A command-line tool that can be used to send test emails to your email server.
   • Mail-Debug: A command-line tool that can be used to debug your email server and provide information about incoming and outgoing emails.

Some common commands to check on servers that are sending emails include:

• telnet <server_ip> 25: Connects to the email server using Telnet and sends a test email.
• swaks -s <server_ip> -f <from_email> -t <to_email>: Sends a test email to the email server using Swaks.
• dig <domain_name>: Checks the DNS records of the sending server.
• nslookup <domain_name>: Checks the DNS records of the sending server.
• mail -s "Test email" <to_email>: Sends a test email to the email server using the Mail command.

Note: The above commands are just examples and may need to be modified to fit your specific email server configuration.