relay/README.md

Chatmail services optimized for Delta Chat apps

This repository helps to setup a ready-to-use chatmail server comprised of a minimal setup of the battle-tested postfix smtp and dovecot imap services.

The setup is designed and optimized for providing chatmail accounts for use by Delta Chat apps.

Chatmail accounts are automatically created by a first login, after which the initially specified password is required for using them.

Deploying your own chatmail server

To deploy chatmail on your own server, you must have set-up ssh authentication and need to use an ed25519 key, due to an upstream bug in paramiko. You also need to add your private key to the local ssh-agent, because you can't type in your password during deployment.

We use chat.example.org as the chatmail domain in the following steps. Please substitute it with your own domain.

1. Install the cmdeploy command in a virtualenv

    git clone https://github.com/deltachat/chatmail
    cd chatmail
    scripts/initenv.sh
   

2. Create chatmail configuration file chatmail.ini:

    scripts/cmdeploy init chat.example.org  # <-- use your domain 
   

3. Point your domain to the server's IP address, if you haven't done so already. Verify that SSH root login works:

    ssh root@chat.example.org   # <-- use your domain 
   

4. Deploy to the remote chatmail server:

    scripts/cmdeploy run
   

   This script will check that you have all necessary DNS records. If DNS records are missing, it will recommend which you should configure at your DNS provider (it can take some time until they are public).

Other helpful commands:

To check the status of your remotely running chatmail service:

scripts/cmdeploy status

To display and check all recommended DNS records:

scripts/cmdeploy dns

To test whether your chatmail service is working correctly:

scripts/cmdeploy test

To measure the performance of your chatmail service:

scripts/cmdeploy bench

Overview of this repository

This repository drives the development of chatmail services, comprised of minimal setups of

• postfix smtp server
• dovecot imap server

as well as custom services that are integrated with these two:

• chatmaild/src/chatmaild/doveauth.py implements create-on-login account creation semantics and is used by Dovecot during login authentication and by Postfix which in turn uses Dovecot SASL to authenticate users to send mails for them.

• chatmaild/src/chatmaild/filtermail.py prevents unencrypted e-mail from leaving the chatmail service and is integrated into postfix's outbound mail pipelines.

There is also the cmdeploy/src/cmdeploy/cmdeploy.py command line tool which helps with setting up and managing the chatmail service. cmdeploy run uses pyinfra-based scripting in cmdeploy/src/cmdeploy/__init__.py to automatically install all chatmail components on a server.

Home page and getting started for users

cmdeploy run also creates default static Web pages and deploys them to a nginx web server with:

• a default index.html along with a QR code that users can click to create accounts on your chatmail provider,

• a default info.html that is linked from the home page,

• a default policy.html that is linked from the home page.

All .html files are generated by the according markdown .md file in the www/src directory.

Refining the web pages

scripts/cmdeploy webdev

This starts a local live development cycle for chatmail Web pages:

• uses the www/src/page-layout.html file for producing static HTML pages from www/src/*.md files

• continously builds the web presence reading files from www/src directory and generating html files and copying assets to the www/build directory.

• Starts a browser window automatically where you can "refresh" as needed.

Emergency Commands to disable automatic account creation

If you need to stop account creation, e.g. because some script is wildly creating accounts, login to the server with ssh and run:

    touch /etc/chatmail-nocreate

While this file is present, account creation will be blocked.

Ports

Postfix listens on ports 25 (smtp) and 587 (submission) and 465 (submissions). Dovecot listens on ports 143 (imap) and 993 (imaps). nginx listens on port 8443 (https-alt) and 443 (https). Port 443 multiplexes HTTPS, IMAP and SMTP using ALPN to redirect connections to ports 8443, 465 or 993. acmetool listens on port 80 (http).

Delta Chat apps will, however, discover all ports and configurations automatically by reading the autoconfig XML file from the chatmail service.

Email authentication

chatmail servers rely on DKIM to authenticate incoming emails. Incoming emails must have a valid DKIM signature with Signing Domain Identifier (SDID, d= parameter in the DKIM-Signature header) equal to the From: header domain. This property is checked by OpenDKIM screen policy script before validating the signatures. This correpsonds to strict DMARC alignment (adkim=s), but chatmail does not rely on DMARC and does not consult the sender policy published in DMARC records. Other legacy authentication mechanisms such as iprev and SPF are also not taken into account. If there is no valid DKIM signature on the incoming email, the sender receives a "5.7.1 No valid DKIM signature found" error.

Outgoing emails must be sent over authenticated connection with envelope MAIL FROM (return path) corresponding to the login. This is ensured by Postfix which maps login username to MAIL FROM with smtpd_sender_login_maps and rejects incorrectly authenticated emails with reject_sender_login_mismatch policy. From: header must correspond to envelope MAIL FROM, this is ensured by filtermail proxy.

Migrating chatmail server to a new host

If you want to migrate your chatmail server to a new host, follow these steps:

1. Block all ports except 80 and 22 with firewall on a new server.

   To do this, add the following config to /etc/nftables.conf:

#!/usr/sbin/nft -f

flush ruleset

table inet filter {
    chain input {
        type filter hook input priority filter; policy drop;

        # Accept ICMP.
        # It is especially important to accept ICMPv6 ND messages,
        # otherwise IPv6 connectivity breaks.
        icmp type { echo-request } accept
        icmpv6 type { echo-request, nd-neighbor-solicit, nd-router-advert, nd-neighbor-advert } accept

        tcp dport { ssh, http } accept

        ct state established accept
    }
    chain forward {
        type filter hook forward priority filter;
    }
    chain output {
        type filter hook output priority filter;
    }
}

Then execute nft -f /etc/nftables.conf as root.

This will ensure users will not connect to the new server and mails will not be delivered to the new server before you finish the setup.

Port 22 is needed for SSH access and port 80 is needed to get a TLS certificate. They are not used by Delta Chat or by other email servers trying to deliver the messages.

2. Point DNS to the new IP addresses.

   You can already remove the old IP addresses from DNS. Existing Delta Chat users will still be able to connect to the old server, send and receive messages, but new users will fail to create new profiles with your chatmail server.

3. Setup the new server with cmdeploy.

   This step is similar to initial setup. However, because ports Delta Chat uses are blocked, new server will not become usable immediately. If other servers try to deliver messages to your new server they will fail, but normally email servers will retry delivering messages for at least a week, so messages will not be lost.

4. Firewall all ports except ssh (22) on the old server. Existing users will not be able to connect from now on and no more messages will be delivered to your old chatmail server.

   Blocking users from connecting to the new server until mailboxes are migrated is needed to avoid UID validity change. If Delta Chat connects to the new server before it is fully set up, it will lose track of the IMAP message UID and miss messages that arrived during migration.

   Same for SMTP port 25, you want it blocked during migration so no new mails arrive while the server is moving.

5. Use rsync -avz over SSH to copy /home/vmail/mail from the old server to the new one preserving file permissions and timestamps.

6. Unblock ports used by Delta Chat and SMTP message exchange. For that you can modify /etc/nftables.conf as follows:

#!/usr/sbin/nft -f

flush ruleset

table inet filter {
    chain input {
        type filter hook input priority filter; policy drop;

        # Accept ICMP.
        # It is especially important to accept ICMPv6 ND messages,
        # otherwise IPv6 connectivity breaks.
        icmp type { echo-request } accept
        icmpv6 type { echo-request, nd-neighbor-solicit, nd-router-advert, nd-neighbor-advert } accept

        tcp dport { ssh, smtp, http, https, imap, imaps, submission, submissions } accept

        ct state established accept
    }
    chain forward {
        type filter hook forward priority filter;
    }
    chain output {
        type filter hook output priority filter;
    }
}

Execute nft -f /etc/nftables.conf as root to apply the changes.