We have two JIRA servers that we synchronize between them, the users between the two JIRA are not the same, the users would like to tag user on other JIRA (they know their account names  and email addresses), how can implement such sync.

I looked into this:

mergeComments—with custom formatting - Exalate Documentation - Exalate Documentation (idalko.com)

But not sure how to merge a comment in a way the notifies the tagged user by email as result of sync.