So many sites and individuals want emails to add to mailing lists. People are wise to this and are often only willing to participate if they can use a bullshit email. Some sites have the "we send a confirmation email, which gets you through the next phase" meaning the email must be valid.....but there's a way round that too, it's called Trashmail. Valid but temporary.
People are sick of spam, they have been for years......they will do everything they can to protect themselves from it. That means not revealing their real emails. Personally when I sign up to a website, I rarely give my proper email at first....I use a throwaway one. That way if it gets flooded with spam, I can discard it and my real one is still clean (as it was before). If after a while their use of my throwaway email matches their promises and I have an ongoing use for the site, I change it to me real one in the options.
My pet hate is the sites that require you to sign up to see what your signing up for.....only to find it wasn't what you thought and you never use it again....these are prime candidates for the "we only want active emails to spam" types.
Sulz is right though, it will cut down your comments......it's a judgment call.