msmtp with iCloud account doesn't work

I'm very new to Linux (Raspbian at Raspberry Pi 4 Model B) and I just try to send an e-mail via command line. Right now, this is working with msmtp and a gmx.de account following this guide. apt-get update && apt-get upgrade -V apt-get install msmtp msmtp-mta mailutils > **/etc/msmtprc** and **~/.msmtprc** contains # Set default values for all following accounts. defaults port 587 tls on tls_trust_file /etc/ssl/certs/ca-certificates.crt logfile ~/.msmtp.log # Mail account account my_name@gmx.de host mail.gmx.net from my_name@gmx.de auth on user my_name@gmx.de password PASSWORD account default : my_name@gmx.de aliases /etc/aliases > **/etc/aliases** contains root: my_name@gmx.de default: my_name@gmx.de > **/etc/mail.rc** contains set sendmail="/usr/bin/msmtp -t" **1. Test** echo "Content of the e-mail" | mail -s "Subject" my_name@gmx.de This works pretty well! But if I change this to my iCloud account the authentication fails (password is correct ;)). # Set default values for all following accounts. defaults port 587 tls on tls_trust_file /etc/ssl/certs/ca-certificates.crt # Mail account account my_name@icloud.com host smtp.mail.me.com from my_name@icloud.com auth on user my_name@icloud.com password PASSWORD account default : my_name@icloud.com aliases /etc/aliases **2. Test** pi@raspberrypi:~ $ echo "Content of the e-mail" | mail -s "Subject" my_name@icloud.com msmtp: authentication failed (method PLAIN) msmtp: server message: 535 5.7.8 Error: authentication failed msmtp: could not send mail (account default from /home/pi/.msmtprc) mail: Sending data to /usr/bin/msmtp -t failed: Process exited with a non-zero status mail: cannot send message: Process exited with a non-zero status Is there anything I can do now? Any help is appreciated!