Mails sent to James server are spooled but they are not processed and sent out.
The issue is similar to the one faced by Zach.
The server seems to be working fine for a few hours or few days, but some time all the mails are spooled but they will not be processed and sent out. Restarted the server several times and some time a few of the mails will be processed and all the others are lost.
As Norman suggested I have took a jstack trace.
Please let me how we can resolve this issue