Then create a web, create users in to the web. How to do this can be read in the documentation found in the ISPCOnfig adminpanel. I don't know how to configure thunderbird, but the smpt / pop3 server is your server / the server's official IP / and dns-name pointing to that ip, the username is the one you created to the according mailadress, the same with the password.
Thank you, my mistake was that i allowed only two users. I have now changed it to the number of users i needed. It is working very well all the mails are coming in but i can only access them through webmail, and i cannot retrieved them from outlook express. I have even activate home_mailbox = Maildir/ in /etc/postfix/main.cf but it still not working. I get the following message: Sending of password did not succeed. Mail server .... responded: chdir Maildir failed.
I guess you used the wrong username in outlook. The username has the form web[ID]_username and is not identical with the email address. Also make sure that you enabled maildir in ISPConfig if you use courier or dovecot as mail daemon.
