Parce que pour du send only, postfix est overkill

SSMTP, c'est juste deux fichiers de conf:

# /etc/ssmtp/ssmtp.conf -- a config file for sSMTP sendmail.
#
# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.
root=adresse_mail
# The place where the mail goes. The actual machine name is required
# no MX records are consulted. Commonly mailhosts are named mail.domain.com
# The example will fit if you are in domain.com and you mailhub is so named.
mailhub=mail.gandi.net:587
# Where will the mail seem to come from?
#rewriteDomain=y
# The full hostname
hostname=locahost.localdomain
# Use SSL/TLS before starting negotiation
UseTLS=Yes
UseSTARTTLS=Yes

# Username/Password
AuthUser=adresse_mail
AuthPass=password

# Email 'From header's can override the default domain?
FromLineOverride=yes

#/etc/ssmtp/revaliases
# sSMTP aliases
#
# Format: local_account:outgoing_address:mailhub
#
# Example: root:your_login@your.domain:mailhub.your.domain[:port]
# where [:port] is an optional port number that defaults to 25.
root:adresse_mail:mail.gandi.net:587