Firewalls

Firewalls, routers, and proxy servers are software and/or hardware which lie between a server machine (or server program) and the external network.

ISMail can be used on machines protected by firewalls, routers, or proxy servers. However, these systems must be configured to allow external machines to access port 25 (SMTP) on the mail server machine in order to send and receive mail. Also, access to port 110 (POP3) and/or port 143 (IMAP4) must be allowed.

Once access to these ports has been enabled, connectivity from the external network to the server can be tested as follows:

• Start ISMail and the SMTP and POP3 servers
• From the machine running ISMail, run the 'telnet' program as follows:
  • telnet domain 25
  • telnet domain 110
  • telnet domain 143
• From the machine on the external network, run the 'telnet' program as follows:
  • telnet domain 25
  • telnet domain 110
  • telnet domain 143

where 'domain' is your domain name or IP address. Each telnet session establishes a connection with either the SMTP (port 25), POP3 (port 110), or IMAP4 (port 143) server. Each server will print a message in the telnet window, indicating it is operating. If you see a message, just disconnect from the server.

If you do not see a message and you are running telnet from the machine running ISMail, it is likely that firewall software is blocking access to the port. See the documentation for the firewall software for specific instructions on allowing access to the port.

If you do not see a message and you are running telnet from a machine on the external network, it is likely that a firewall, router or a proxy server is blocking access to the port. See the documentation for the firewall, router, or proxy server for specific instructions on allowing external access to the port.

Also, see Troubleshooting to help check these configuration settings.