This started in the last week or so...

550 SC-001 Mail rejected by Windows Live Hotmail for policy reasons. Reasons for rejection may be related to content with spam-like characteristics or IP/domain reputation problems. If you are not an email/network admin please contact your E-mail/Internet Service Provider for help. Email/network admins, please visit http://postmaster.live.com for email delivery information and support
Connection closed by foreign host.

My IP is in the 74.82.3.0/24 subnet.

I have SPF set up (and have for years) for my domain and have both my Linode IP listed as well as another, older server that I still use. That older server can still deliver mail to hotmail just fine.

I filed a complaint with Hotmail/Live, but in the interim have modified my Sendmail configuration on my CentOS box to relay mail destined to hotmail through my older server:

/etc/mail/mailertable:

.hotmail.com    smtp:[IP]
hotmail.com     smtp:[IP]

So now at least I have a workaround...

I'm not clear why Hotmail is flagging my Linode IP. Perhaps it's something about the entire subnet as I'm the only user who sends mail from my Linode IP address (personal emails only, nothing bulk) and it's definitely not been compromised...

I did the senderid@microsoft.com thing too, so maybe hotmail will magically start working again at some point.

Edit: Anyone else on the same subnet as me having problems?

See this thread.