The rainbow table would just need to include alphanumeric letters + '@' for up to 30 letters. I think your emails are in nearly every rainbow table in existence.
Still, I don't think I've ever had a rainbow table that contained plaintexts longer than 12 characters. Are 30+ length tables common these days?
You’re correct that brute force with an entropy of 3 per bit would still be too big for rainbow table usage (like 10^15 PB too big).