On my newly setup Excalibur box I receive cron mails as
Content-Transfer-Encoding: quoted-printable which makes reading them
with mail(1) unpleasant.

Using mail(1) itself or just printf'ing to /usr/sbin/sendmail mails are
not send as quoted-printable.

Here is an example bad mail:

#v+
Message 1:
>From kt@??? Tue Jan 06 09:54:02 2026
Envelope-to: kt@???
Delivery-date: Tue, 06 Jan 2026 09:54:02 +0100
From: root@??? (Cron Daemon)
To: kt@???
Subject: Cron <kt@x280> backup mobile: -Lahv
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
X-Cron-Env: <HOME=/home/kt>
X-Cron-Env: <PATH=/home/kt/.local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin>
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <LOGNAME=kt>
Date: Tue, 06 Jan 2026 09:54:02 +0100

ssh: connect to host mobile port 22: Connection refused=0D
#v-

How can I turn this off?

#v+
root@x280:~# more /etc/default/cron
# Cron configuration options

# Whether to read the system's default environment files (if present)
# If set to "yes", cron will set a proper mail charset from the
# locale information. If set to something other than 'yes', the default
# charset 'C' (canonical name: ANSI_X3.4-1968) will be used.
#
# This has no effect on tasks running under cron; their environment can
# only be changed via PAM or from within the crontab; see crontab(5).
READ_ENV="yes"

# Extra options for cron, see cron(8)
#
# For example, to enable LSB name support in /etc/cron.d/, use
# EXTRA_OPTS='-l'
#
# Or, to log standard messages, plus jobs with exit status != 0:
# EXTRA_OPTS='-L 5'
#
# For quick reference, the currently available log levels are:
# 0 no logging (errors are logged regardless)
# 1 log start of jobs
# 2 log end of jobs
# 4 log jobs with exit status != 0
# 8 log the process identifier of child process (in all logs)
#
EXTRA_OPTS=""

root@x280:~# more /etc/default/locale
# File generated by update-locale
LANG="C.UTF-8"

t@x280:~# more /etc/environment
root@x280:~#
#v-