Hello, First of all thank you for your help and attention. I do not why I can not enter to websites and receive or send mails using Thunderbird (Webmail works fine) from a computer connected to the same local network than the server (Ubuntu server 18.04 with PHP 5.6, PHP 7.0, PHP 7.1, PHP 7.3 and PHP 7.4) in which is installed ISPConfig. Maybe I have some bad configuration in ISPConfig? I attached the HTF report because I exedeed the maximum amount of characters. Thank you!