This is a practical guide for setting up an email server for personal or small groups use. It does not contain many explanations, but includes links to more detailed references where possible.
While a lot of the contents are generic, for simplicity it will use:
This guide will use the following data for illustration purposes, replace them with your own where appropriate.
example.com.198.51.100.7.2001:db8::7.Note IPv6 is optional but highly encouraged, and supported by most providers.
You first need to have a server to use. This could be an existing one (for example, if you already have one where you host HTTP), doesn't have to be exclusive for email.
In this guide we will use a separate server, mostly for clarity.
For small groups the size of the server does not matter, any small VPS (virtual private server) will do just fine.
Specifically for hosting email servers, there are some things to check when selecting a provider:
Remember to update your server regularly, setting up unattended upgrades is highly recommended.
Set up the following DNS records for example.com. This is usually done
either in your DNS server, or in the user interface of your DNS provider.
; Assign "mail.example.com" to the server's IP addresses.
; Replace these with the ones for your server.
mail A 198.51.100.7
mail AAAA 2001:db8::7
; The mail server for example.com is mail.example.com.
@ MX 10 mail
; Use SPF to say that the servers in "MX" above are allowed to send email
; for this domain, and nobody else.
@ TXT "v=spf1 mx -all"
Finally, you should go to your server provider and configure the "reverse DNS" (also known as "PTR") for the IP addresses to be to "mail.example.com". This is important, as some spam checkers will consider it a factor.
References: A record, MX record, Sender Policy Framework (SPF).
TLS certificates are needed to send and receive email securely. letsencrypt will provide us with a free certificate, which needs to be renewed every 90 days, so the following relies on automatic renewal.
Note certbot is the recommended letsencrypt command line client.
sudo apt install certbot acl
# Obtain a TLS certificate for mail.example.com.
sudo certbot certonly --standalone -d mail.example.com
# Give chasquid access to the certificates.
# Dovecot does not need this as it reads them as root.
sudo setfacl -R -m u:chasquid:rX /etc/letsencrypt/{live,archive}
# Automatically restart the daemons after each certificate renewal.
sudo mkdir -p /etc/letsencrypt/renewal-hooks/post
cat <<EOF | sudo tee /etc/letsencrypt/renewal-hooks/post/restart
#!/bin/bash
systemctl restart chasquid
systemctl restart dovecot
EOF
sudo chmod +x /etc/letsencrypt/renewal-hooks/post/restart
First, install dovecot, and let chasquid use it for authorizing users. That way, you will only use a single system for managing users (dovecot).
sudo apt install dovecot-imapd dovecot-pop3d dovecot-lmtpd
cat <<EOF | sudo tee /etc/dovecot/conf.d/11-chasquid.conf
# Allow chasquid to authorize users via dovecot.
service auth {
unix_listener auth-chasquid-userdb {
mode = 0660
user = chasquid
}
unix_listener auth-chasquid-client {
mode = 0660
user = chasquid
}
}
EOF
You will need to configure dovecot authentication depending on your needs.
For example, if you want to use only system users, or virtual users.
See the /etc/dovecot/conf.d/10-auth.conf file, and the dovecot
documentation for more
details.
sudo apt install chasquid
sudo setfacl -R -m u:chasquid:rX /etc/chasquid/
# Use the certificates obtained from certbot.
sudo mv /etc/chasquid/certs/ /etc/chasquid/certs-orig
sudo ln -s /etc/letsencrypt/live/ /etc/chasquid/certs
# Make chasquid accept mail for "example.com".
sudo mkdir -p /etc/chasquid/domains/example.com
# Tell chasquid to deliver local mails to dovecot, and use it for
# authentication.
cat <<EOF | sudo tee -a /etc/chasquid/chasquid.conf
# Deliver email via lmtp to dovecot.
mail_delivery_agent_bin: "/usr/bin/mda-lmtp"
mail_delivery_agent_args: "--addr"
mail_delivery_agent_args: "/run/dovecot/lmtp"
mail_delivery_agent_args: "-f"
mail_delivery_agent_args: "%from%"
mail_delivery_agent_args: "-d"
mail_delivery_agent_args: "%to_user%"
# Use dovecot authentication.
dovecot_auth: true
EOF
With this configuration, chasquid will use dovecot to manage users, so refer to the dovecot documentation for the details.
You can also add chasquid-specific users with chasquid-util user-add.
To make chasquid manage an additional domain otherdomain.com, first add the
following records to otherdomain.com:
@ MX 10 mail.example.com
@ TXT "v=spf1 mx -all"
Then, tell chasquid about it by running mkdir
/etc/chasquid/domains/otherdomain.com. Don't forget to restart it afterwards.
Alternatively, you can use a different MX record, as long as you can get chasquid a certificate for it.
apt install spamassassin spamc.apt install clamdscan.That's all it takes. chasquid default hooks will pass incoming mail through both if (and only if) they are installed.