Hi, ISPCONFIG 3.1.15p1 ubuntu 18.04 TLS After installing all my configuration, it's seems that postfix not work like i want. (i can't connect in smtp) what i do : in main.cf make 2 link for the SSL : smtpd.cert -> /etc/letsencrypt/live/MYDOMAIN.com/fullchain.pem smtpd.key -> /etc/letsencrypt/live/MYDOMAIN.com/privkey.pem myhostname #myhostname = ns31573xx.ip-xx-xx-xxx.eu myhostname = mail.MYDOMAIN.com the result of hostname -f in SSH is : ns31573xx.ip-xx-xx-xxx.eu i add DNS Record : Type A | Name : mail | Data : xx.xx.130.115 type MX | name : MYDOMAIN.com | Data : mail.MYDOMAIN.com. my file /etc/hosts.allow is empty i see some people adding 127.0.0.1 localhost ... i don't test this in isp config, i have create 4 mail box with MYDOMAIN.COM like [email protected] in outlook i can't connect smtp. i have put in config pop : mail.MYDOMAIN.com port 143 TLS smtp : mail.MYDOMAIN.COM port 587 TLS smtp doesn't work. if i try a connexion with ROUNDCUBE, i can see some mail error, and i can't send email (loop box sending ...) the error of return mail is : host ASPMX.L.GOOGLE.com[2a00:1450:400c:c07::1a] said: 550-5.7.1 [2001:41d0:203:6473::] Our system has detected that this message does 550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and 550-5.7.1 authentication. Please review 550-5.7.1 anyone can help me ? thank you !