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Self-hosted server for Protonmail client.

This project is not affiliated or supported by ProtonMail.

What is it?

Neutron is a server that will allow the ProtonMail client to be used with backends. Several backends are available right now:

  • IMAP: this will read and store messages on your IMAP server. Received messages will stay as is (that is, unencrypted) but messages saved from the web client will be encrypted. You will login to the web client with your IMAP username and password.
  • SMTP: this will send messages using your SMTP server. Messages are sent encrypted to the server. If a recipient's public key is not found, the server will decrypt the message before sending it to this recipient.
  • Filesystem: settings, contacts, keys are stored on disk. Keys are always stored encrypted.
  • Memory: all is stored in memory and will be destroyed when the server is stopped.

Neutron is modular so it's easy to create new backends and handle more scenarios.

Keep in mind that Neutron is less secure than ProtonMail: most servers don't use full-disk encryption and aren't under 1,000 meters of granite rock in Switzerland. Also, SRP is not yet supported (#35). If you use Neutron, make sure to donate to ProtonMail!



See config.json. You'll have to change IMAP and SMTP settings to match your mail server config.

	"Memory": {
		"Enabled": true,
		"Populate": false, // Populate server with default neutron user
		"Domains": [""] // Available e-mail domains
	"Imap": { // IMAP server config
		"Enabled": true,
		"Hostname": "",
		"Tls": true,
		"Suffix": "" // Will be appended to username when authenticating
	"Smtp": { // SMTP server config
		"Enabled": true,
		"Hostname": "",
		"Port": 587,
		"Suffix": "" // Will be appended to username when authenticating
	"Disk": { // Store keys, contacts and settings on disk
		"Enabled": true,
		"Keys": { "Directory": "db/keys" }, // PGP keys location
		"Contacts": { "Directory": "db/contacts" },
		"UsersSettings": { "Directory": "db/settings" },
		"Addresses": { "Directory": "db/addresses" }


To generate keys for a new user the first time, just click Sign up on the login page and enter your IMAP credentials.


  • -config: specify a custom config file
  • -help: show help



  • Go (to build the server)
  • Node, NPM (to build the client)
# Get the code
go get -u
cd $GOPATH/src/

# Build the client
git submodule init
git submodule update
make build-client

# Start the server
make start


make build-docker
docker build -t neutron .
docker create -p 4000:4000 -v $PWD/config.json:/config.json -v $PWD/db:/db neutron


All backends must implement the backend interface. The main backend interface is split into multiple other backend interfaces for different roles: ContactsBackend, LabelsBackend and so on. This allows to build modular backends, e.g. a MessagesBackend which stores messages on an IMAP server with a ContactsBackend which stores contacts on a LDAP server and a SendBackend which sends outgoing messages to a SMTP server.

Writing a backend is just a matter of implementing the necessary functions. You can read the memory backend to understand how to do that. Docs for the backend are available here:



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