A telnet to the smtp port of your server works fine for me:
server1:~# telnet quentasweb.com 25
Connected to unn-251.superhosting.cz.
Escape character is '^]'.
220 quentasweb.com ESMTP Postfix (Debian/GNU)
250-AUTH LOGIN PLAIN
Connection closed by foreign host.
Is it maybe your workstation firewall/router firewall that blocks you?