Solved: Send Mail with external Mail Client (Thunderbird) I have a running mail server, that means that https://domain.tld:81/webmail can send mails without problems. For downloading mails in Thunderbird i use the following settings: Server: domain.tld Port: 110 User: web1_root For sending Mails i use Server: domain.tld Port: 25 User web1_root Security: No But i cannot send Mails (as said: webmail works). What is wrong? I am pleased to receive answers. PS: I searched in older Postings, too. PS.S: It worked in the past, but i forgot how the settings for thunderbird were.