Zoom and firewalls.

[LPBBEAR]

7. Your issue is not firewall related.

"First things first – your emails. Stop using the CC line for multiple recipients. (Seriously, right now!)
An illustration. You send out an email to your congregation using the CC function. The email goes out to all recipients, with all email addresses being seen by all recipients"

You're confusing "Firewalls" with an email issue in your post.

Email applications give you a couple sending options.

1. CC or Carbon Copy
By using this option you are sending an email to multiple recipients. Unfortunately when you use this option you are exposing all addresses to ALL recipients. Beyond the obvious privacy issues some viruses can read these lists of exposed recipients. If a recipient in your list of CC'd recipients has a system infected with a computer virus its possible it may pick up all exposed email addresses and begin to self send virus infected emails to all listed recipients.

2. BCC or Blind Carbon Copy
This option is usually available and is the better choice. It also sends to all recipients but does not expose all recipients to each other. A better option for privacy and security.