sSMTP

wikipedia:ssmtp

/etc/ssmtp/ssmtp.conf

echo "My first email" | ssmtp [email protected]
ssmtp: Authorization failed (535 5.7.8  https://support.google.com/mail/?p=BadCredentials p12sm1383020wrr.10 - gsmtp)

• If using Gmail: https://www.google.com/settings/security/lesssecureapps

See also

• Mail, SMTP, submission, SMTPS, POP, IMAP, StartTLS, Exim, Postfix, IRedMail, Fail2ban, Dovecot, Roundcube, DKIM, SPF, DMARC, MX, ssmtp, mailx, Swaks
• Mail, email: Postfix, mail, SMTP, LMTP, POP3, IMAP, mailutils, amavis, Gmail, iCloud, ssmtp, msmtp

https://serverfault.com/a/672182