I am also having the problem where I am not receiving all messages sent from forms on my sites. Dreamhost support is claiming it's because of their spoofing policy, however, my forms have been working for years and in fact last worked on February 9th. The e-mail messages are sent using the e-mail address entered by the visitor and it has worked this way for years. I happened to test the form on the 11th and found it wasn't working. Now today, it works, sometimes, and it doesn't matter if the "from" e-mail is my dreamhost-hosted address, or not.
I have not changed anything in my code, and I'm still working with Dreamhost support to try to find the real problem. If it used to work and now doesn't, and I haven't changed any code, it has to be a issue with the servers.
Also, the spoofing reasoning doesn't really make sense to me. If I have a form that sends e-mail to me, and it's from whatever address the user enters (valid, or not), how can that be considered spoofing? I'm getting information from the user. All messages come to me (at my dreamhost e-mail account) and if I'm allowing a user to put in an e-mail address that hardly the idea behind spoofing.