Configurer envoi de mails postfix

Bonsoir tout le monde !

Depuis un bon moment je cherche à configurer Postfix. J'aimerais bien utiliser le SMTP de gmail mais que ce soit envoyé avec mon nom de domaine.
Voici la configuration de main.cf :

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname
 
#smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
#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
 
readme_directory = no
 
# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
 
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
 
myhostname = cpmtech.fr
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
#myorigin = /etc/mailname
mydestination = cpmtech.fr, www.cpmtech.fr, localhost.cpmtech.fr, localhost
relayhost = ssl://smtp.gmail.com
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
mailbox_command = procmail -a "$EXTENSION"
#smtp_sasl_auth_enable = yes
#smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
#smtp_sasl_security_options = noanonymous
 
 
#Restrictions
smptd_helo_required = yes
strict_rfc821_envelopes = yes
 
#Requirements for the HELO statement
# smtpd_helo_restrictions =
# permit_mynetworks,
# permit_sasl_authenticated,
# reject_non_fqdn_hostname,
# reject_invalid_hostname,
# permit
 
#Requirements for the sender details
smtpd_sender_restrictions =
        permit
#
#Requirements for the connecting server
smtpd_client_restrictions = permit
#       permit_mynetworks,
#       permit_sasl_authenticated,
#       reject_rbl_client sbl-xbl.spamhaus.org,
#       reject_rbl_client lsit.dsbl.org,
#       permit
 
#Requirements for the recipient address
#smtpd_recipient_restrictions = permit, reject_unknown_recipient_domain
#       reject_unauth_pipelining,
#       permit_mynetworks,
#       permit_sasl_authenticated,
#       reject_non_fqdn_recipient,
#       reject_unknown_recipient_domain,
#       reject_unauth_destination,
#       permit
 
# SASL SUPPORT FOR SERVERS
#
# The following options set parameters needed by Postfix to enable
# Cyrus-SASL support for authentication of mail servers.
#
#smtp_sasl_auth_enable = yes
#smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd.db
#smtp_sasl_security_options =mydomain = localdomain
mydomain = localdomain

Lorsque j'ai un mail à envoyer, il se retrouve dans la file d'attente, avec un message d'erreur en status : unknown mail transport error

J'espère que certains pourront m'aider !!
Si vous avez des questions je suis disponible.

Merci