Since our target is for March of early next year (JBoss World Atlanta), we will likely make it JDK 5.0. This will also allow us to use annotations more effectively and eliminate most XML wiring throughout our architecture and prepare us for 2.0 which I hope to incorporate more NIO into.
I'd like to speak with you if this is a problem and get a better understanding of why. There are some horrible bugs in JDK 1.42's garbage collection and JD5 is actually more stable as a result in most environments (and having worked on the consulting side I have large system production experience to back that statement up). We still support 1.42 now so this is still up for discussion if there is a solid technical reason. However, 1.5 is even available on the Mac now (long overdue) and AIX.
The reason I am asking is becuase the client I am consulting at right now does not have a migration plan to JDK 5.0 yet and the application I'm building for them will be deployed to JDK 1.4.2. They are considering using JBoss Mail but if it is dependent on JDK 5.0 they will not. The reason they don't have a plan to move to JDK 5.0 is because they don't see other application server vendors moving toward JDK 5.0 (in spite of the benefits).
Okay but that's now. For final release I'm talking March. The other appserver vendors will have production release on 5.0 out by then. I think the just release WebLogic runs on JDK 5 and JRockit 5 has been out for awhile. IBM will be the slowest mover as always but if they want to maintain their JEE certification they will have to move. They better be REAL close by then since JEE 5 spec is slated for December. Moreover they already have a 5.0 of their JDK for AIX and friends.
Moreover, JBMS 1.0 will only run on JBoss as it directly uses various microkernel services. If this is a mail based application then it is one thing where appserver might be a consideration. If it is a mail server then who care's what connection pool implementation we're using (JBoss or WebSphere). Anyhow, running anything but JBAS cannot be a consideration for 1.0. In the future we may base it on the new microcontainer (thus be portable), but we're mostly interested in performance, scalability, compatibilty (with standards-based mail clients/protocols) and ease of installation/management/configuration for 1.0.
Since to support mid to high end servers (4 or more cpus) we need parallel garbage collection that works and doesn't lock up, even if we didn't REQUIRE JDK 5.0 for JBMS 1.0 I'd be real cranky with folks who hobbled themselves. Nearly as cranky as I am with folks who say "JBoss is unstable" only to find out they're on 1.3.1 still (you don't even want to know what the GC/Hotspot bugs were in that sucker).
Anyhow, I'll be happy to talk to them for you and scare them into JDK 5 if it helps.