msmtp

if you just want something super lightweight on a system to send out e-mails using existing SMTP services such as amazon ses or mailgun etc.:

installation

apt-get install msmtp

configuration

put the following into /etc/msmtprc and make your updates

defaults
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
add_missing_from_header on
syslog         on

account        dreamland
host           smtp.example.com
port           465
tls_starttls   off
from           user@example.com
user           user@example.com
password       superSecure

account default : dreamland

aliases               /etc/aliases

sendmail drop-in

save the following as /usr/sbin/sendmail (and replace the e-mail with the one you use as from from above)

#!/bin/sh
sed '0,/^\r\?$/ { s/^To:.*/To: user@example.com/ }' | /usr/bin/msmtp "$@"

send e-mails using msmtp

echo -e "Subject: test mail\r\n\r\nSup, is a test mail." | msmtp hello@example.com

mongosh multipass