In this lobby discussion ( https://raddle.me/f/lobby/31758/anarchist-designed-communication-platform ) it links to a project by anarchists to set up a communication platform.
I'm not sure if I should be writing this post here or in the /f/Anarchism forum, but as far as I know most of the options they might want already exist.
First, use the Tor Project ( https://www.torproject.org/ ) to make your internet traffic more difficult to trace. An attacker or eavesdropper can tap your connection at the telephone pole and watch how much data you send and receive but not the content or the recipient.
Second, running your own email server is somewhat complex but manageable with patience and research https://mailinabox.email/ If your recipients are using a centralized proprietary email server then it won't work, because Google, Microsoft, Comcast, Apple, or whoever can read everything. But if I host mine and you host yours, our servers can connect directly through TOR with TLS encryption and only we can read the content. (There is also encrypted email through PGP software, but it's awkward to use.)
Third, there are alternative free software social networks like Diaspora ( https://diasporafoundation.org/ ), Friendica ( https://friendi.ca/ ), GNU Social ( https://gnu.io/), Mastodon ( https://mastodon.social/about )