Is this so that admins can open tickets with an email address not assigned to an existing client? Right now non-clients can create tickets if allowed, but staff cannot create tickets for unregistered users.

yes so that staff can create ticket to a possible client who may have came to our live chat or may be any reference which came from another existing client to contact his friend as well etc .

I endorse this option also.

Please add this.

So I had this problem recently. I wanted to email a client to get them to register for an account on Blesta and soon realised that I couldn't. I had to send the email from my POP3 mailbox instead.
It's just one reason of many why I still use a POP3 mailbox for my support desk - this way I can send emails out to non-registered clients and when they reply, it goes back to the support desk and creates a ticket!
Of course, I lose the original message that I sent, so this feature request would be much appreciated please.

+1 for this

Sometimes, someone comes with a reference and we have his/her email address to contact. So, there should be an option to create a support ticket for non users email address.

Another +1 to add to this list, we use an external support system, and not having this within Blesta means we need to continue with the two separate systems