Here's a list of disposable email domains if you'd really like to block them: https://github.com/lavab/disposable

I would go one step further and look for {spam_words} in "username+{text}@{googledomain}.com", where spam_words can be "junk", "spam", etc. This is like a very narrow edge case, but still might catch something. Again, if you're into that kind of thing; I'm quite skeptical that it brings any value.