You want to block it from sending to specific email addresses or to block it from sending to email addresses at all? For GJ you can disable Email inviting within GJ > Config > Groups > Invites and remove "Email" from "Invite By". For CB Invites you can't stop it from sending emails as that's its point (to invite people to join the site). There is no feature to block from sending to a list of email addresses in either of those.

We need a way to block from sending to specific email addresses.

There's no feature to do this.

The main reason is that we had someone send to a known 'honeypot' email address (don't ask why ... they are users ... what can I say).

Honeypot email addresses for the most part change hourly, daily, weekly, or monthly. So there's really no stopping this even if you could supply it a list of email addresses.

Just wondering how others are preventing potential spam issues like this?

You can't prevent this. There's no real way to stop issues between the keyboard and chair except educate the user. It's pretty strange for someone to email a spam list email address and had to be on purpose and if that's the case you should consider banning the user. Nobody just accidentally emails a honeypot address as they're obscure for a reason and hidden inside of source code so bots pick them up and wouldn't make any sense to a human.

If the user that did this is a spam registration you can look into using CB AntiSpam to help protect against spam registrations. You can also add Captcha to the invite features to help avoid spamming.