Don't think so, but I found a form to fill in for M$ and now have this reply:
Thank you for writing to the Sender ID Management Team. This is Mike and I am responding to your request for the enrollment to the Sender ID program. I appreciate your interest in joining this program.
We have added your xxx.com and xxx.biz to the Sender ID program. This may take up to 2 business days to be fully replicated in our systems. If you have any questions regarding this please let me know.
We reviewed your SPF record and note that it includes the "ptr" or reverse DNS lookup mechanism. The specification for SPF records (RFC 4408) discourages use of "ptr" for performance and reliability reasons. This is especially important for Windows Live Mail, Hotmail and other large ISPs as a result of the very high volume of mail we receive each day. We highly recommend you remove the "ptr" mechanism from your SPF record and, if necessary, replace it with other SPF mechanisms that do not require a reverse DNS lookup, such as "a", "mx", "ip4" and "include." This will help ensure that Sender ID validation is performed as accurately as possible, maximizing your email deliverability while protecting your domain from spoofing.
You do not need to notify us when you make this or any revision to your SPF record since we will automatically pull the current record from the DNS daily. Thanks again for your support in improving online trust and confidence.
You can find technical information on the Sender ID program at
Sender ID Home Page
Regards,
Mike C.
Sender ID Management Team
I'm speaking to my hosters to see if they can cast any light on this. What are the implications of removing reverse DNS lookup?