main.cf

    mydomain_fallback = localhost
    message_size_limit = 0
    biff = no
    mynetworks_style = subnet # was only seen by localhost

    mynetworks = 127.0.0.0/8, [::1]/128
    #mynetworks = 127.0.0.0/8, 192.168.1.0/24

    smtpd_client_restrictions = permit_mynetworks permit_sasl_authenticated permit
    recipient_delimiter = +
    smtpd_tls_ciphers = medium
    inet_protocols = all
    inet_interfaces = all
    config_directory = /Library/Server/Mail/Config/postfix
    virtual_alias_domains = $virtual_alias_maps
    virtual_alias_maps = $virtual_maps
    recipient_canonical_maps = hash:/Library/Server/Mail/Config/postfix/system_user_maps
    smtpd_enforce_tls = no
    smtpd_use_pw_server = yes
    relayhost = [mail.X.pt]:25
    smtp_fallback_relay = [cpanel.X.pt]:25
    smtpd_tls_cert_file = /etc/certificates/Server Fallback SSL Certificate.6D8408A85A861E9E7AE1A6CDE19A336CE8A4DBB0.cert.pem
    mydomain = X.pt
    smtpd_pw_server_security_options = cram-md5,digest-md5,gssapi
    smtpd_sasl_auth_enable = yes
    smtpd_helo_required = yes
    smtpd_tls_CAfile = /etc/certificates/Server Fallback SSL Certificate.6D8408A85A861E9E7AE1A6CDE19A336CE8A4DBB0.chain.pem
    content_filter = smtp-amavis:[127.0.0.1]:10024
    smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reject_unauth_destination
    header_checks = pcre:/Library/Server/Mail/Config/postfix/custom_header_checks
    myhostname = remote.X.pt
    smtpd_helo_restrictions = reject_non_fqdn_helo_hostname reject_invalid_helo_hostname
    smtpd_use_tls = yes
    smtpd_tls_key_file = /etc/certificates/Server Fallback SSL Certificate.6D8408A85A861E9E7AE1A6CDE19A336CE8A4DBB0.key.pem
    enable_server_options = yes
    mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
    mailbox_transport = dovecot
    smtp_sasl_password_maps = hash:/Library/Server/Mail/Config/postfix/sasl/passwd
    smtp_sasl_auth_enable = yes

    ######Edit######

    ###To send (SMTP)###
    # to avoid 550 error SMTP AUTH
    smtp_sasl_security_options =

    smtp_sender_dependent_authentication = yes
    sender_dependent_relayhost_maps = hash:/Library/Server/Mail/Config/postfix/relayhost/maps