I wonder how many of them are the same people who feel the first amendment should be repealed because free speech can hurt some peoples feelings or hear opinions/information that doesn't conform to how they want the world to be.

> We reject mails which fail the SPF check immediately within the mail session

Try doing this as a colo/hosting provider servicing thousands of domains and hundreds of thousands of incoming emails (if not millions a day) from all all over the world and you quickly learn that immediately rejecting by SPF is something that can really only be done by small companies who get very little mail from few sources.

It's just not something a support desk is ready to handle since your hosting customers want the ability to send email from wherever is convenient so rarely want an SPF record in their own domain, and will scream bloody murder if you bounce "important" email because someone buggered an SPF record or never had one in the first place because they've never had anyone else reject their mail over it.

It's just not a viable option for large scale email/hosting.

Now as part of a scoring scheme like spamassassin, that's a different beast. Then it becomes at least slightly useful.

Some do. I know of a guy who runs a very large free webemail service as a means to gather accurate addresses to spam. Everynight he harvests the days logs of outgoing emails and adds new ones to his master list. He also has access to the logs of a few ISPs where his "buddies" work and they pass on the logs from their systems as well and he harvests from there as well. You don't always have to signup, or give the email address to anyone except people who you want to to email you for someone to find out your address and add it to a spam list.