Thanks Victor for your answer. Well in this case with my configuration I don't need to specify in the GUI which kind of encryption... I've tried with this configuration with gmail, hotmail, yahoo and another private server that doesn't need the encryption and it's always working with the same configuration:
smtpd_tls_cert_file = /etc/postfix/smtpd.cert smtpd_tls_key_file = /etc/postfix/smtpd.key smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtpd_tls_CAfile = /etc/postfix/cacert.pem smtpd_tls_auth_only = no smtpd_tls_security_level = may smtpd_sasl_security_options = noanonymous smtpd_sasl_tls_security_options = noanonymous smtpd_tls_received_header = yes smtpd_tls_loglevel = 1 smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache smtp_tls_CAfile = /etc/postfix/cacert.pem smtp_tls_cert_file = /etc/postfix/smtpd.cert smtp_tls_key_file = /etc/postfix/smtpd.key smtp_use_tls = yes smtp_tls_scert_verifydepth = 9 smtp_tls_loglevel = 1 smtp_sasl_tls_security_options = $smtp_sasl_security_options smtp_sasl_tls_verified_security_options = $smtp_sasl_security_options smtp_sasl_auth_enable = yes smtp_sender_dependent_authentication = yes If somebody can see some errors in this configuration, please let me know... Thanks Michele