supported dictionary type: smtp.gmail.com

I'm trying to setup postfix inside a Docker container. On startup I'm running the following setup script:

# Install postfix/mailutils with configuration options
echo "postfix postfix/mailname string $MAILSERVER:587" | debconf-set-selections
echo "postfix postfix/main_mailer_type string 'Internet Site'" | debconf-set-selections
apt-get install -yqq postfix
apt-get install -yqq mailutils

# Setup credentials for SMTP server
mkdir -p /etc/postfix/sasl
touch /etc/postfix/sasl/sasl_passwd /etc/postfix/main.cf
echo "[$MAILSERVER]:587 $EMAIL_USER:$EMAIL_PASSWORD" >> /etc/postfix/sasl/sasl_passwd
chown -R postfix:postfix /etc/postfix
chmod 600 /etc/postfix/sasl/sasl_passwd
postmap /etc/postfix/sasl/sasl_passwd

# Create postfix configuration 
echo "relayhost = [$MAILSERVER]:587" >> /etc/postfix/main.cf
echo "smtp_sasl_auth_enable = yes" >> /etc/postfix/main.cf
echo "smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd" >> /etc/postfix/main.cf
echo "smtp_sasl_security_options = noanonymous" >> /etc/postfix/main.cf
echo "smtp_use_tls = yes" >> /etc/postfix/main.cf
echo "debug_peer_list = $MAILSERVER" >> /etc/postfix/main.cf
echo "debug_peer_level = 3" >> /etc/postfix/main.cf
echo "smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt" >> /etc/postfix/main.cf

# Reload postfix for new configurations to take effect
postfix reload
/etc/init.d/postfix restart

After running the script I end up with the following at the end of my /etc/postfix/main.cf:

# Use gmail
relayhost = [smtp.gmail.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_use_tls = yes
debug_peer_list=smtp.gmail.com
debug_peer_level=3
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

I have confirmed that /etc/postfix/sasl_passwd and /etc/ssl/certs/ca-certificates.crt exist but I keep getting:

postfix/bounce[1052]: error: unsupported dictionary type: smtp.gmail.com

Note: I have seen questions with similar titles but the solutions posted haven't helped with my setup.