The reason why SMTP stopped working? I don't Know…
How I solved it? In "Services" -> "Squid Proxy Server" -> "ACLs" i went to the field "Unrestricted IPs" and set my LAN net in CIDR Format (192.168.1.0/24), then I went to the field "ACL SSLPorts" and set this "2096 587 443 563"
After saving, aplying and a reboot, the SMTP was working again.
Greetings!