External email with OVH mail on proxmox

configure the /etc/postfix/main.cf like the below

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

#CHANGEME
myhostname=proxmox1.gatom.net

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
#mydestination = $myhostname, localhost.$mydomain, localhost
#relayhost =
mynetworks = 127.0.0.0/8
inet_interfaces = loopback-only
recipient_delimiter = +

compatibility_level = 2

# OVH SMTP/TLS
relayhost = [ssl0.ovh.net]:465
smtp_use_tls=yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_sasl_security_options = noanonymous

smtp_tls_wrappermode = yes
smtp_tls_security_level = encrypt

the two last are required for SMTPS or error message is :

(TCP port 465) requires setting "smtp_tls_wrappermode = yes", and "smtp_tls_security_level = encrypt" (or stronger)

add credentials to /etc/postfix/sasl_passwd

 [ssl0.ovh.net]:465     login:password

set permissions

chmod 600 /etc/postfix/sasl_passwd

create the password db

postmap /etc/postfix/sasl_passwd

of the db is not correct with the given credentials, error is

(SASL authentication failed; server ssl0.ovh.net[193.70.18.144] said: 535 5.7.1 Authentication failed)

install the package for sasl

apt-get install libsasl2-modules

otherwise error is

(SASL authentication failed; cannot authenticate to server ssl0.ovh.net[193.70.18.144]: no mechanism available)

restart postfix

systemctl restart postfix

test

echo "test ok" | mail -s "Test" dest-email@domain.com