Hi Rinu,
In terms of Licenses there are currently two version of Jentrata, one is essentially a fork of Hermes and remains under the GPL license the other version which currently only support ebms3/AS4 is licensed under Apache 2.0. The goal is to add support to ebms 2 and AS2 in the new version of Jentrata.
So what does that mean for derivate works if you use the old hermes version of Jentrata and you plan to redistribute it you will need to provide the source code for any changes you make. Since the new version is licensed under the ASL 2.0 you are free to redistribute as you see fit as along as it maintains the original copy write.
Now depending on your plans I would strongly suggest you consider contributing directly the core project (am always looking for new contributors to the project) So feel free to fork the project on GitHub and send a pull request with your changes
let me know if you have any more questions or want more details on contributing
cheers
Aaron