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.
Think about it this please:
If a user “majid” does not exist on your Jira system, how would you tag him there manually? Would that be possible? If the Jira API allowed that, you can do that via Exalate as well. AFAIK this would not be possible.
If you want to really think out of the box here, what you can do is type in the full email address of the person you want to tag, and Exalate transports that over to the destination. On the dest side, you can use regular expressions within the script to isolate the email address and find the user corresponding to that email - but its poor UX in my opinion.
which is your source system and which one target ?like is it Jira on-prime → Jira cloud ? or other combination ?
In original question , it is mentioned that email address are known. But in your case what is the common thing ? like the email address can be same but not the domain or display name is same or any property which is identical in both the systems?