I configured Outlook to use port 25 on my ISP's smtp server. That works fine and I can send email. But if I try to use the server in one of my applications (using JavaMail), I can't connect to the server. Same thing if I try to "manually" telnet to it: I get
telnet: Unable to connect to remote host: Connection refused
How is this possible? And how do I configure my application to be able to send mail?
Edit to add more information:
Wireshark shows that when Outlook tries to send email, it connects to port 25 of the ISP's smtp server. Everything works as expected. When I try 'telnet server 25', the connection never makes it to the server. I see 'Destination unreachable (Communication administratively filtered)', which seems to indicate the firewall at my workplace blocked it. If that's the case, how does the firewall know to let Outlook through?