Why not download Tails OS and make a tutanota/protonmail account and send it from there? Neither tuta nor proton are really the best choice anonymity-wise, but will be sufficient if used with Tails, but will also not be stuck in some spam filter (unlike cock.li for example). Tails is an operating system, which can be run from an USB-Stick and doesn't need you to install anything (except Tails itself on said USB-Stick). All traffic in Tails is routed through the Tor network, a network which aims to protect your anonymity, without anyone you have to trust involved. If you want a safer option than protonmail or tutanota respectively, I recommend Disroot, but I couldn't sign up, so I'm not sure if it will work for you.
You boot into Tails, open Tor Browser, create an account on either protonmail or tutanota, send your email and nobody knows who it was. I doubt anybody in this forum will do this for you, if it's for you already such a big thing. Maybe at least say what it's about, because I doubt anyone is willing to send mails to news agencies about some sensitive stuff from a complete stranger.
https://tails.net/ - The agnostic incognito live system
https://disroot.org/en - probably the best option for anonymous, private E-Mail, albeit has problems with signing up and spam filters
https://proton.me/mail - less reputable option, but supports sign up over Tor and is mostly guaranteed to not go into the spam filter
https://mail.tutanota.com/ - also an E-Mail provider, which allows sign up over Tor
- a video about how to use Tails
- another video on Tails
Additional steps to ease the paranoia are:
- using public wifi
- when using public wifi, spoofing your mac address (Tails does this automatically)
- using Whonix over Tails (requires better computer specs, is more difficult to use and setup)
- disabling javascript where possible
- not using personally indentifiable information in your mail
