Good morning for everyone! I have a behavior than I can not solved in a server with (Ubuntu 12.04.5 LTS (Precise Pangolin)) ISPConfig 18.104.22.168p5. The server has every service (web, panel, mail, dns, db). The behavior occurs specifically for the mail server when trying to connect via webmail (roundcube and squierrelmail) and email clients like thunderbird and outlook. When the squirrelmail trying to access e gives the following error: 530 5.7.0 Must issue a STARTTLS command first When I configured the roundcube in the following ways: SMTP SSL (465), SMTP STARTTLS (587) and SMTP (25) and IMAP (143) and IMAPS (993). None of the above let me enter the account and does not show me any error. When I set up thunderbird imap smtp port 25 and port 143, I can download the mails, but when I try to send an email, repeats the error: 530 5.7.0 Must issue a STARTTLS command first When I set up thunderbird STARTTLS SMTP imap port 587 and port 143, I can download the mail but when I try to send an email, I get the error that I can not connect to the server. (The port 587 is allowed in both firewalls, server and border) The only way I could send mail from thunderbird is with SSL SMTPS (465). I already check the configuration of the master.cf and main.cf file server problems, I will compare with files from other mail servers that have it running and are practically identical in configuration. I tried to disable STARTTLS configuration with the following parameters and restart the postfix service but continued behavior, that is I can not connect from squirrelmail or roundcube and I can not send mails without SSL. smtp_use_tls = no smtpd_use_tls = no smtp_tls_security_level = may smtpd_tls_security_level = may If anyone has any idea about how to resolve this behavior is the greatly appreciate it. I will do several tests more and I will attach the logs.