Debian12.8 ; Let's Encrypt, WEB/Mail Server SSL

1.  Obtain a certificate (Let's Encrypt)

1.1 advance preparation

1.Enable mod_ssl

2.Package management system Snappy installed
Since the SSL certificate issuing tool "certbot" of Let's Encrypt is recommended to be installed using "snap" after 2021, install Snapd first.

Bring snapd version up to date

Version Check

1.2.certbot package install

Create symbolic link to /snap/bin/certbot

Confirmation

1.3 Obtain a Let's Encrypt Certificate

It is assumed that a web server such as Apache httpd or Nginx is running.
If the web server is not running on the server where the work is to be performed, follow the procedure below under "Obtaining a Let's Encrypt certificate when the web server is not running".
It is also assumed that the server on which the work is to be performed (the server with the FQDN of the server from which you want to obtain the certificate) is accessible from the Internet at port 80.

#First time only, you must register your e-mail address and agree to the Terms of Use Specify an e-mail address that can receive your messages.

「Successfully received certificate.」

# The following certificate is obtained under [/etc/letsencrypt/live/[FQDN]/] as described in the message

# cert.pem
#chain.pem
# fullchain.pem
# privkey.pem

Obtaining a Let's Encrypt certificate when the web server is not running
It is a prerequisite that the server on which the work is to be performed is accessible from the Internet at port 80.
#Use the simple Web server function by specifying [--standalone].
# -d [FQDN from which you want to obtain a certificate]
　FQDN (Fully Qualified Domain Name) : Hostname. Domain name without abbreviation
# If there are multiple FQDNs for which you want to obtain certificates, specify multiple -d [FQDNs for which you want to obtain certificates]

1.4 Automatic renewal of certificates (Let's Encrypt)

①Pre-registration testing
First, test the automatic renewal using the following --dry-run option. With this option, the certificate is not renewed, but only the operation is tested, so there is no need to worry about being caught by the limit on the number of times a certificate can be obtained.

②When you install the snap version of certbot, the automatic certificate renewal function is also installed.

snap.certbot.renew.timer is registered
Check the unit file for snap.certbot.renew.timer

According to the above settings, it will attempt to update at 3:33 and 18:16 every day as specified in the OnCalender parameter (however, the set time will change randomly for each update).

Check the unit file snap.certbot.renew.service

However, the web server that uses the certificate will not be restarted, so set up a script that will run automatically after the update

2. SSL/TLS (Let's Encrypt) configuration for Apache2

①Edit Apache2 SSL-related configuration files
hoge.com-ssl in hoge.com-ssl.conf is an arbitrary name

②Reflecting and activating the configuration file

③http to https redirect

One of the following methods

④Reflection of settings and startup
If you chose to fill in vhost-yourdomain.conf above

Apache Restart

3. SSL/TLS (Let's Encrypt) settings on the mail server

3.1 Obtaining a certificate for the mail server

Obtain a certificate for the mail server, but it cannot be obtained in the same way as above, so the following with the "--standalone" option fails.

If I stop the web server once and then do it, it succeeds as follows

3.2 Postfix Configuration

3.3 Dovecot Configuration

Allow Port 587

3.4 Thunderbird Settings

Incoming server

Port  :  143
Connection security   :  STARTTLS
Authentication method  :  Normal password

Sending server

Port   :  587
Connection security   :  STARTTLS
Authentication method  :  Normal password