LANG=pl_PL.UTF-8
LC_CTYPE="pl_PL.UTF-8"
LC_NUMERIC="pl_PL.UTF-8"
LC_TIME="pl_PL.UTF-8"
LC_COLLATE="pl_PL.UTF-8"
LC_MONETARY="pl_PL.UTF-8"
LC_MESSAGES="pl_PL.UTF-8"
LC_PAPER="pl_PL.UTF-8"
LC_NAME="pl_PL.UTF-8"
LC_ADDRESS="pl_PL.UTF-8"
LC_TELEPHONE="pl_PL.UTF-8"
LC_MEASUREMENT="pl_PL.UTF-8"
LC_IDENTIFICATION="pl_PL.UTF-8"
LC_ALL=pl_PL.UTF-8

/bin/echo -e "Subject: Mail z routera ASUSrnrn<text with Polish characters>" |/opt/bin/msmtp --debug --from=default -t my_user@gmail.com,my_user@other.domain

defaults
tls on
tls_starttls on
tls_trust_file /opt/etc/certs/ca-bundle.crt

account default
host smtp.gmail.com
port 587
auth on
user my_account@gmail.com
password xxxxxxxx
from my_account@gmail.com
#logfile /opt/msmtp.log