The following is a list of email services hosted in hidden services to send and receive anonymous email through Tor.
Always remember that you will not have a clue about who the administrators are. It might be the NSA, a scammer, someone without technical competence or someone wonderful who really cares about your privacy. Trust nobody, email messages should always be encrypted using your own private encryption keys.
Lelantos (http://lelantoss7bcnwbv.onion/): Paid anonymous Tor based email account that allows you to create over 100 different aliases, email PGP encryption using your own keys, self-destructing messages that will autodelete when they reach the specified date, and support for SMTorP, mail relying over the Tor network to communicate with other email services that work in Tor.
TorBox (https://torbox3uiot6wchz.onion): There is no connection in between TorBox and the clearnet, this is a Tor only email service allowing people to communicate with other TorBox users, you can’t send messages to Yahoo or Gmail. The person you would like to communicate with will have to sign up for a TorBox email address too.
Mail2Tor (https://mail2tor2zyjdctd.onion): Free anonymous email service with webmail (SquirrelMail), POP3, IMAP and SMTP. It can send email to addresses out of the Tor network using relays, no important logs or emails are stored in any of those servers in case they are seized, they only contain Tor and mailing software, user data is stored encrypted in a hidden Tor node which IP is not known.
BitMessage (http://bitmailendavkbec.onion/): Webmail gateway to connect Bitmessage with email, this is a free service that can be accessed through clear net or a Tor hidden node, a basic understanding of privacy technologies is required to understand how BitMessage works.
RiseUp: Their hidden tor services include a shell account, XMPP server and an email account, accessible in the clearnet as well as their Tor hidden service. RiseUp is a USA based privacy provider for left leaning political activists. Accounts are only given with two referrals from two different RiseUp account holders or if you are part of a political group sharing their aims.
Austici: Italian based collective fighting what they call fascism, racism, militarism and sexism. They manage Tor hidden services that include anonymous email and IRC chat. Accounts are only granted to those sharing their political ideas.
Tip: If you don’t have Tor installed in your computer and want to visit a .onion website without being anonymous use https://onion.to/