On Sender-ID and SPF
Just as a warning: Don’t expect me to either implement SPF or Sender-ID.
Both have just been accepted as experimental standards by the IETF. But both also have problems and therefore I don’t want to implement them.
For SPF it’s mind boggling that it has been accepted as standard. It essentially breaks the ability to forward mail: If you send me an email to one of my old adresses, they are sent to my current one with a .forward. That will not work anymore with the current SPF implementations, because the mail seems to be coming from the old server, instead of your mail server. And of course, you also lose the ability to roam freely with your laptop and use any mailserver you are entitled to use as a guest user, because those are not in your SPF DNS records.
Sender-ID seems to `solve’ the first problem of SPF by adding a PRA header (Purported Responsible Addres), which essentially says: “From Sender on behalf of From”, where the PRA encodes the Sender part. This seems like a nice idea, except that Microsoft patented this idea and then sent it to the IETF as standard. And since Microsoft has not taken an official stance as to whether they will enforce this patent, and my mail will probably pass through the United States, I’m not going to take any chances.
And Microsoft is now also pulling a monopoly-like stunt: If your e-mail does not have a Sender ID, Microsoft wants to junk your message