Most of those old folders are safe to remove. ie: Keep the 2 most recent folder versions/the one symlinked to. You can delete those config.#####, not a whole lot of room freed up on it, but for tidying up purposes.
If you're cleaning out your /opt/zimbra/.saveconfig/ folder however be a little more careful. Sub-folders for old configs is one thing, but I wouldn't suggest removing your current config.save, etc ;)
Those tracking: Bug 23414 - Clean up stale files and folders on upgrade
Good blog article to read: Open Source Product Management: How do features get into Zimbra?Quote:
Note: Enhancement and bug requests also funnel in through the same ticketing process.
Support Incidents determined to be enhancement requests or bug reports do not count against your allotted Support Incidents.