How do I send emails via msmtp from inside XEN DOM0

I have a XEN server with someVMs, one of them is the email server. How do I tell DOM0 to send all root emails to my administration email, which is inside the email-VM? I tried install msmtpd and added the config file /etc/msmtprc:

# A system wide configuration file is optional.
# If it exists, it usually defines a default account.
# This allows msmtp to be used like /usr/sbin/sendmail.
account default

# The SMTP smarthost
host mail.myOtherVM.de

# Use TLS on port 465
port 587
tls on
tls_starttls on

# Construct envelope-from addresses of the form "user@oursite.example"
from %U@oursite.example

# Syslog logging with facility LOG_MAIL instead of the default LOG_USER
syslog LOG_MAIL

But When trying to send an email with echo -e "Subject: msmtp test\nhello test." | msmtp rubo77@mydomain.de on my email VM I get the error:

lost connection after DATA from unknown[2a01:xxxx:1d02::2]
disconnect from unknown[2a01:xxxx:1d02::2] ehlo=2 starttls=1 mail=1 rcpt=0/1 data=0/1 commands=4/6

(I also tried port 465 but that one is not open at all.)