relayhost = smtp.fastwebnet.it:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

smtp.fastwebnet.it      myusername@fastwebnet.it:pass

Sep  2 16:35:30 server1 postfix/cleanup[11161]: 26AC92820A0: info: header Subject: asd from local; from=<root@server1.org> to=<testuser@gmail.com>
Sep  2 16:35:30 server1 postfix/cleanup[11161]: 26AC92820A0: message-id=<20170902143529.v25nffla7mczfpss@server1.org>
Sep  2 16:35:30 server1 postfix/qmgr[11150]: 26AC92820A0: from=<root@server1.org>, size=425, nrcpt=1 (queue active)
Sep  2 16:35:32 server1 postfix/smtp[11158]: SSL_connect error to smtp.fastwebnet.it[85.18.95.132]:587: -1
Sep  2 16:35:32 server1 postfix/smtp[11158]: warning: TLS library problem: error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:../ssl/record/rec_layer_s3.c:1399:SSL alert number 40:
Sep  2 16:35:32 server1 postfix/smtp[11158]: 26AC92820A0: to=<testuser@gmail.com>, relay=smtp.fastwebnet.it[85.18.95.132]:587, delay=1.9, delays=0.12/0/1.8/0, dsn=4.7.5, status=deferred (Cannot start TLS: handshake failure)