I'm not aware of any known issues with outbound mail in those versions (There is an issue with POP/IMAP in 5.0.6 under very specific conditions - https://jira.atlassian.com/browse/JRA-28543 ).
You've listed a precise set of actions here that you don't get emails for (close, create, comment, etc). Are you getting notification emails being sent for other actions, or are these just the particular ones you tried?
If there are no emails going out from JIRA at all, you could try troubleshooting the SMTP settings:
1) From any JIRA screen, type "gg" to bring up the admin quicksearch
2) Type "Outgoing Mail" (or part thereof) and press enter.
3) Next to the mail server details, click "Send a test email" and go through the process of sending a test email. If this fails, it should provide more useful troubleshooting details.
Otherwise, if that sends OK, it's possible another administrator has messed around with the JIRA notification settings without your knowledge. To check the notification settings for a project:
1) From any JIRA screen, type "gg" to bring up the admin quicksearch
2) Type the name of your project and press enter.
3) Click the "Notifications" tab on the left-hand side.
It should list all the actions (Issue Created, Issue Updated, etc) with the people who will be notified with them. If instead it says "There are currently no notifications for this project." then click Actions->Select a Scheme and pick a different notification scheme.
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