First of all, outside of a legal fiduciary relationship where privacy of communications is legally enforced, if you send something to someone in an email, they have every right to make it public if they so choose. If you don't want the things you say to be public, then don't send them to other people. That's exactly what happens with people whose nude pictures get put on the internet. If you don't want them on the internet, don't send them.
Second, this isn't just two private people. These are people on an elected board of directors of a non-profit that owes a duty to its members and donors. So emails relating to the business of that entity are much more a matter of public interest than a private email between two friends. Someone who was a board member of the organization has every right to disseminate that email if they believe it to have been inappropriate.
I've served on boards of non-profits, and would never send a "very ugly" email about other people to other board members. I wouldn't write-it unless I would be willing to defend it to the people who are the subjects of it. And if a fellow board member or officer drafted a "very ugly" email that would bring the organization into disrepute, then that is a negative comment on that person's fitness to be involved in the organization.
But the final point I'd make is this -- don't you wonder what it was that was said in that email that caused all of this? Imagine what whomever it was must have said for it to have this kind of repercussions. Apparently, it was bad enough that it has resulted in a changing control over the organization. So, I'd suggest that if someone is going to complain about a board member sending it to the Cruz campaign, perhaps they should just make it public so we can all judge who the real bad guy is here.
This is the logic of a Stalinist Cruzer who thinks that just because the rules permit something, that it is okay. Most normal people would be very upset if their private communications are spread, and rightly so. Even more bizarre is that these private communications were being shared with a political campaign, and then that campaign reacted by attempting to punish these individuals through their minions on the board. This is the realm of big brother and massive political thuggery.
and would never send a "very ugly" email
More than likely, since you are a very ugly Cruzer, you have probably made some very ugly posts on FR. Mind telling me where you work at, what charitable organizations you work with, so I can catalog and start sending all your online statements to them?