Install an openfire instance for each domain…and then setup the SRV record in DNS for each server. this will allow the servers to find each other… Once that is done, you can use s2s
Can you please be more specific about SRV records of each domain and once it is added, if at all i am login to spark for domain abc.com and want to chat with another user of domain xyz.com.
if you have step by step information kindly share.