Resolve ticket by email

[John Shin]

Is there any keyword # that can be used to resolve or close ticket?

[Florian]

Try to enter the transition name in the mail body. So when you have a [Close] button on you issue action bar, just send the word close. 
This might work. I think I have seen this before. Obviously this will not work when there is no valid transition for status A to status B. 

[Quoc Nghia_ TRAN]

You can define the rule at Projects/<<Project Name>>/Project settings/Automation

For example below: When the receiving email body contains these words, JSD will update the status of ticket.