Sorry, I don't know whether this question is suitable to be posted here. My friend give me an smtp client program written in java. When new data inserted in the database, the smtp client program will send an email out using my newly installed zimbra server. The program and zimbra server are at different location and connected through Internet. Before this, the program worked fine by using another mail server with different domain mail. Now, the email stuck in the database and cannot send to the zimbra server. I already modified the program variable as bleow so that it can work with the zimbra server. = pop3
mail.transport.protocol = smtp = =
mail.from =
IP =

The zimbra server alone work fine and can be used with mail client like OE and Thunderbird. My question is why the smtp program cannot send mail using zimbra server. I also wonder why there is no authentication in smtp program but can work before. In this condition, the smtp program relay to the zimbra server?