Remailers: Send Emails without Registration
An anonymous remailer is: :
... a server that receives messages with embedded instructions on where to send them next, and that forwards them without revealing where they originally came from. There are Cypherpunk anonymous remailers [archive], Mixmaster anonymous remailers [archive], and nym servers [archive], among others, which differ in how they work, in the policies they adopt, and in the type of attack on anonymity of e-mail they can (or are intended to) resist.
In Whonix-Workstation ™, remailers can be used over Tor. The goal is access to a cheap tool that can send messages without registration, rather than offering more anonymity for (web) messages than Tor can provide.
In theory, remailers are high latency networks that should provide more security than using low latency networks like Tor in isolation; see Anonymity Network for further details. However, the unfortunate reality is there are no known high latency networks which meet the following criteria at the time of writing (2019):
- Development: active development is indicated by regular:
- developer commits addressing bugs, maintenance and design improvements
- press releases and blog posts
- forum/mailing list activity
- Infrastructure: users have reliable access to multiple servers.
- User Base: a significant population regularly utilizes remailers for (pseudo)-anonymous messages.
In practice, the dearth of users and servers means it is safest to assume that remailers provide little to no additional anonymity. Whonix developers would welcome a rebirth of high latency networks and an active, sizable user/developer community, but this is an unlikely outcome in the near-medium term.
Table: Remailer Recommendations
If remailers are not careful, various attacks are possible when attempts are made to send mail/messages.
Table: Remailer Threats 
|Adversary Threat Model||
|Size and Distinguishability||
Mixmaster: Tor Remailer
Mixmaster remailers do several things: 
- They send a message to another e-mail address or post it to a news group.
- They accept encrypted messages with instructions for processing hidden inside the encrypted envelope.
- They strip all mail headers.
- They add new headers such as subject lines.
- They remove some information from the end of the message.
- They encrypt part of a message using a key specified in the message.
Interested readers are still free to peruse the Mixmaster documentation. Historical tests with this software were successful -- when utilizing one remailer, mail/messages took between 10-120 minutes before arriving in the recipient's inbox.
Third Party Web Interface
As noted earlier, Tor Browser can be paired with a third party web interface. However, this configuration is less secure and should be used with care because the server administrator is capable of snooping on cleartext as it is typed or pasted.
- German Privacy Foundation (awxcnx) email [archive]
- German Privacy Foundation (awxcnx) usenet [archive]
- Webmixmaster paranoici (clearnet SSL) [archive]
- W3- Anonymous Remailer (clearnet) [archive]
- Anonymouse (clearnet, German website) [archive]
- send-email.org (clearnet) [archive]
- NGZ-Server.de (clearnet, SSL) [archive]
Note: Readers are welcome to correct any inaccuracies in this section.
The Wikipedia Cypherpunk anonymous remailer [archive] article and list of Cypherpunk remailer services [archive] suggests these services utilize Mixmaster. Online, associated help files  also explain that it is safer to use Mixmaster, since Cypherpunk remailers just provide an email based interface.
Since the full list of type I and type II remailer servers  reveals that most type I (Cypherpunk) are also type II (Mixmaster) servers, it does not appear necessary to learn and document how Cypherpunk remailers work. In fact, it does not appear to be an actual alternative, since Cypherpunk remailers cannot be used if Mixmaster is non-functional for some reason. This option would also defeat the purpose of this wiki entry (sending mail without registration), since it still requires a mail provider.
Footnotes / References
- https://en.wikipedia.org/wiki/Anonymous_remailer [archive]
- Those who believe remailer chains will improve anonymity are free to disregard this advice and create a path length of their choosing.
- https://mason.gmu.edu/~afinn/html/tele/components/anonymous_remailers.htm [archive]
- This can be averted by exchanging public keys in person and on disk, downloading public keys over a secure website, or using a digital signature certificate from a qualified company.
- Or experience network outages.
- By including a random ID number for each hop.
- Tracing a message forward requires an adversary to capture the message and then send many copies to the first remailer. When multiple, identical messages emerge from the remailer and move to the next hop, the 'bump' in remailer traffic reveals the route it took.
- Broken link: http://www.cypherpunks.to/remailers/help.txt [archive]
- https://remailer.paranoici.org/rlist2.html [archive]