List of email providers (categorized by tor/privacy friendliness).
Note: This list does not say anything about the trustworthiness of the provider itself.
good
http://sofia.ecnetworld.com <--> http://e3qixnonjb76zovy.onion (great provider. You should try it. Supporting multiple identities and send emails with fake identities) - (requires subscription payment)
http://maillvohhojeoliq.onion <--> Great Anonymous Mail Service, always from the ECNET Staff (the same of Sofia Mail System) with multiple networks access, POP3/IMAP free service (required a small donation, no minimal request)
http://xdkriz6cn2avvcr2vks5lvvtmfojz2ohjzj4fhyuka55mvljeso2ztqd.onion/ Cock.li (Very transparent provider, no personal information collected at sign up. Has an onion service and Tor-facing webmail. Requires JS, but uses the open-source RoundCube software. POP3/IMAP support.)
https://mailbox.org (30 days trial for free; see how to use their Tor exit or their mail server Onion site)
https://scryptmail.com (7 days trial for free; webmail only, no POP3/IMAP)
https://riseup.net (registration is limited to invite codes by fellow activists)
https://mail.ru (secondary email is not verified, BAD will lock your account later when using tor, no anon recovery possible; beware: mail.ru develops and spreads spyware called mail.ru guard)
https://cadamail.com/web totally free and easy to register, pop3 + imap, unlimited inbox size, relatively fast, supports sending to most onion mails and works without javascript. http://cadamailgxsy6ykq.onion/web/
~
Mail2Tor: http://mail2tor2zyjdctd.onion/ (not very reliable: Delayed Mail (still being retried), lost connection with 127.0.0.1)
http://secmailw453j7piv.onion (http://secmail.pro) (unreliable, failed to send messages or receive them)
http://torbox3uiot6wchz.onion/ (There is no connection between TorBox and the public internet: All the messages are sent and received within TorBox).
bad
https://protonmail.com (webmail only, no POP3/IMAP, requires verification with other email account)
Unseen.is - https://www.unseen.is/ (requires secondary e-mail address).
fastmail.com (requires SMS verification)
tutanota.com (locks accounts created via tor: https://lists.torproject.org/pipermail/tor-talk/2016-May/040867.html )
Lelantos-Project: lelantoss7bcnwbv.onion (requires subscription payment)
autistici.org:
Javascript must be enabled for the form to work <...> In order to use the services offered by our network, you have to share the basic principles of ... <...> Please tell us why you need this service. <...> Things we are possibly interested about: what type of person are you? What are your activities? How do you relate to our political identity (manifesto)? Why you chose us instead of others? <...> Write anything about anonymity, privacy, the NSA, Linux, open source, cryptography, and the request will be ignored. You can do better than that. All information will be destroyed
openmailbox.org (blocks tor users from creating accounts: Unable to continue. Please contact the administration team (internal error code: 10))