Can I synchronize an instance from behind an enterprise firewall?
I want to synchronize between Jira instances, but they can't communicate directly via http(s) because of my enterprise firewall's strict settings.
Can I still configure a synchronization?
Yes, that's not a problem. You can use Backbone's to server/data center (behind firewall) configuration to set up a synchronization via file exchange or email.
Backbone natively supports PGP encryption for files and emails.