cannot login to mails on a new Postfix mail server

view story

http://stackoverflow.com – I have a problem in my mail server installation, I used Ubuntu 12.04.2 Server Edition + Postfix + Courier, using this tutorial : Here after installation finished i faced a problem with setup mail account on Mozilla Thunderbird mail client that it show problem "Configuration could not be verified --- is the username or password wrong?" & I am sure that i typed it correctly. P.S. : This a local server for test before installation on the real server so I used the ip address for mail server as the server hostname . I tried to use IMAP & POP3 (Port 143, 25) --- SSL : STARTTLS -- Normal pa (HowTos)