Hotmail blocks messages without notice

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Recently some friends of mine using Hotmail accounts complained that I was no longer writing them, or replying to their mails. I checked my mail server logs, and found nothing. At my "home office" I have an ADSL router and I got a fixed IP address. This allows me to run some services (FTP, CVS, etc. ) to access some data while working remotely, and a mail server I setup years ago to keep spam and viruses under control, and use my own domain mail addresses.
I started to trace the connection to Hotmail, and found nothing wrong. Hotmail accepts the message, but it is never delivered.
Hotmail should use SPF DNS records to accept mails - and when it does not find one after accepting the message it drops it without notice! No warning message is returned to the sender. That's a very stupid and arrogant policy. If you a block a message, you're obliged to inform the sender.
When I started to relay mail through my ISP SMTP server message were delivered (I know someone of you thinks "that's what you should have done in the first place" - I had my reason no to do it).
I understand very well the need to fight spam. But blocking any server without an SPF record - which is not a mandatory standard yet - just because it could be a bot-infected machine it's like blocking any Windows machine because almost all bot-infected machines are Windows ones.
Moreover Microsoft itself sells Windows Small Business Server which is a all-in-one server solution, including an Exchange server. Many small business use it on ADSL lines with simple DNS configurations. Are they blocking them too?