Утилита msmtp

# apt install msmtp

# cat /etc/msmtprc

defaults
port 25
tls off
#tls on
auth off

account default

host mail.isp.un
domain server.corpX.un
#from asterisk@server.corpX.un  #need for mutt

#host server.corpX.un
#domain corpX.un
#from root@lan.corpX.un

$ cat mail.txt

Content-Type: text/plain; charset=UTF-8
To: userX@isp.un
From: Asterisk <asterisk@server.corpX.un>
Subject: Record
Запись
cделана

cat mail.txt | msmtp -f asterisk@server.corpX.un userX@isp.un