I propose blocking all access to Joomla's administrator login page and front-end user login (if you don't use it) because I constantly see a-hole bots in my logs trying to hack my site.  Add these lines to the Nginx site configuration.

# DENY ACCESS TO JOOMLA ADMIN
       location ~* /administrator.* {
       deny all;
       }

# DENY ACCESS TO JOOMLA USER LOGIN
       location ~* /component/user.* {
       deny all;
       }

Now how do you access the Joomla administrator login page??  Serve your site on another port using a simpler configuration, then setup your firewall to only allow your IP to access that port.

It's a good idea to match your Zimbra MTA hostname given during an EHLO with the hostname associated with your public IP address.

su - zimbra
zmprov mcf zimbraMtaMyHostname mail.example.com
zmcontrol restart

My domain name registrar offers email aliases and forwarding; however, this feature causes my mail server's SPF checks to fail because the registrar's mail relay sends on behalf of the originating server.  I fixed it by white-listing the registrar's mail relay IP block in SpamAssassin.

Read more: Zimbra - Add Trusted Relay to SpamAssassin

By default Zimbra automatically discards inbound mail that receives a high spam score (aka "super spam").  Although the score is configurable up to 100, this default could cause false positive email to disappear and make troubleshooting spam scoring difficult.

Change the default behavior using these commands:
su - zimbra
zmprov mcf zimbraAmavisFinalSpamDestiny D_PASS
zmprov ms <mta server> zimbraAmavisFinalSpamDestiny D_PASS
zmcontrol restart

Choose from these values:
D_PASS -> Deliver all spam regardless of score
D_BOUNCE -> Generate a bounce message
D_REJECT -> Reject the message
D_DISCARD -> Silently discard the message (default)

THE SITUATION
Some of my end-users do this from time to time: They open an Outlook attachment (such as a Word doc), edit it, save it, then close it.  Where is it!?  It's buried in Outlook's temp file folder, dude!

THE SOLUTION
* Turn OFF "Hide protected operating system files" in Windows Explorer.
* Navigate to this path: C:\Users\USERNAME\AppData\Local\Microsoft\Windows\Temporary Internet Files
* You'll find a folder in there called "Content.Outlook" that should contain the missing files.  If the "Temporary Internet Files" folder appears as a big mess, then try accessing the path via UNC, instead of locally.