SMTP/POP3 through proxy System.getProperties() vs new Properties()?

Question

Im trying to get mail from a POP3 server through a proxy. Most "tutorials" suggest doing something like

 Properties p = System.getProperties();
 p.setProperty("proxySet", "true");//does this line even do anything?
 p.setProperty("socksProxyHost", proxyHost);
 p.setPorperty("socksProxyPort", proxyPort);
 p.setProperty("socksProxyVersion", "5");//or 4 if you want to use 4
 p.setProperty("mail.pop3.socketFactory.class", SSL_FACTORY);
 p.setProperty("mail.pop3.socketFactory.fallback", "false");//also not sure what it does
 p.setProperty("mail.pop3.port", portOnHostYouWantToTalkTo);
 p.setProperty("mail.pop3.socketFactory.port", portOnHostYouWantToTalkTo);

 Session session = Session.getDefaultInstance(p, null);
 //or session = Session.getInstance(p, null);

 URLName urlName = new URLName(protocol, hostYouwantToTalkTo, portOnHostYouWantToTalkTo, null, mailbox, mailboxPassword);
 Store store = session.getStore(urlName);

Now, if I do something like this I get an exception:

java.net.SocketException: Can't connect to SOCKS proxy:Connection timed out: connect.

My POP3 server does not log any connections, suggesting there is a proxy issue or an error in my code. I am using 73.29.157.190:29099 for now.

2) If, however, I do

 Properties p = new Properties();
 //all the same logic and stuff
 Session = Session.getInstance(p, null);

My POP3 server logs a connection from localhost, and works properly, suggesting that I am NOT using a proxy to connect to it and everything else is fine.

My question is, why do "tutorials" use System.getProperties() and pass it to getInstance()? Every Session instance will keep a reference to System.properties. So, effectively every Session instance will be affected every time you try to create a new one or alter System.getProperties() in any way so you might as well reuse the same one.

Does javamail need something set in System.properties specifically and not the ones passed to Session?

Also, what parameters do you need to set in order to get javamail to use a proxy? What does System.properties have that makes it work unlike my new Properties? A link to a good tutorial or documentation that explains it would be greatly appreciated.

Thanks!

Bill Shannon Bill Shannon · Accepted Answer · 2015-01-23T07:59:50

First, get rid of all the socket factory stuff, you don't need it.

Next, make sure you really have a SOCKS proxy and not just a web proxy. If you do, see this JavaMail FAQ entry.

Setting the System properties for a SOCKS proxy will cause all network connections from your program to go through the proxy server, which may not be what you want.

SMTP/POP3 through proxy System.getProperties() vs new Properties()?

1 Answers