Obviously it’s not so difficult to send out emails from a Java EE application via JavaMail. What I am interested in is the best pattern to receive emails (notification bounces, mostly)? I am not interested in IMAP/POP3-based approaches (polling the inbox) – my application shall react to inbound emails.
One approach I could think of would be
- Keep existing MTA (postfix on linux in my case) -> ops team already knows how to configure / operate it
- For every mail that arrives, spawn a Java app that receives the data and sends it off via JMS. I could do this via an entry in /etc/aliases like
myuser: "|/path/to/javahelper"with javahelper calling the Java app, passing STDIN along. - MDB (part of Java EE application) receives JMS message, parses it, detects bounce message and acts accordingly.
Another approach could be
- Open a listening network socket on port 25 on the Java EE application container.
- Associate a SessionBean with the socket. Bean is part of Java EE application and can parse/detect bounces/handle the messages directly.
- Keep existing MTA as inbound relay, do all its security/spam filtering, but forward emails to
myuser(that pass the filter) to the Java EE application container, port 25.
The first approach I have done before (albeit in a different language/setup).
From a performance and (perceived) cleanliness point of view, I think the second approach is better, but it would require me to provide a proper SMTP transport implementation. Also, I don’t know if it’s at all possible to connect a network socket with a bean…
What is your recommendation? Do you have details about the second approach?
Perhaps SubEtha SMTP [edit: now relocated from Google Code to GitHub] would be of interest — it is a Java library that allows your application to receive SMTP mail. I’m about to try it out.
Here’s a somewhat related Stack Overflow question (and someone suggests SubEthaSMP):
What is the easiest way for a Java application to receive incoming email?