Amazon SES Connection

I am trying to use Amazon SES mail service. I have configured settings properly, and with the credentials it is working in one of our network machine, but in other it is not working, alwayz gives ConnectException

javax.mail.MessagingException: Could not connect to SMTP host: email-smtp.us-east-1.amazonaws.com, port: 25;nested exception is:java.net.ConnectException: Connection refused: connect