I just had one!
An email from a perfectly sensible email address, telling me that she worked for Orion films (part of MGM) and they were interested in one of my recent books (which, due to just winning an award, is very high profile). She gave a phone number and asked me to call at my convenience, or to email her as they had items that needed discussion.
I had about ten seconds of excitement before I worked out a few things. Firstly, some of the grammar in the email was questionable (but not everyone has English as a first language, my mind tried to tell me). Secondly, there was no mention of my agent (who deals with all my rights sales). Thirdly, there were mentions of 'being selected' and 'a few other authors', plus telling me how stupendous my book was, without any detail.
So I passed the whole thing onto my agent - who would have to deal with any offers anyway. She's been dealing with Netflix lately on behalf of one of my books, so I did wonder if someone had just bypassed her somehow and come direct to me by mistake. She looked into things in more detail and found out that this is a scam. Apparently they get authors all excited, thinking that a major film studio has offered for a book, then hit them with the 'but you need to pay someone to write a screenplay'. Which, if a genuine studio has offered, is all done in-house. So authors pay out, and all they get is a screenplay which is useless, because any studio want to do things 'their way', is expensive, and probably not very well written.
Ah well. One day I'll be on the big screen.