Vista blocks the EHLO command in SMTP port 25

I cannot send E-mails using SMTP port 25. I have analyzed the problem using
TELNET and found out that Vista blocks the EHLO command but not the HELO
command.
Vista:
TELNET o smtp.galnet.dk 25
220 mail-smtp2.ode.cdnet.dk ESMTP
EHLO MyPC
<timeout>

To verify that the problem is not an ISP issue I have tried exactly the same
using Windows XP:
TELNET o smtp.galnet.dk 25
220 mail-smtp2.ode.cdnet.dk ESMTP
EHLO MyPC
250-mail-smtp2.ode.cdnet.dk
250 ...

The Vista is a Home Edition with no Anti Virus and with a disabled firewall.
Unfortunately my ISP does not support an alternative SMTP port.
My Outlook worked with no problems until ultimo october 2007.
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Thanks