ACS is accusing me of owing them money and they say they are suing me and I will go to court.

I have received several emails from ACS Inc.,,threatening to take me to court and telling me that I will be arrested soon and will have to pay $4206.00. I've been warned to get an attorney and be prepared. It is signed  Mark Smith, Sr. Attorney (ACS, Inc.). I noticed that the email address is a gmail address which I hardly think a professional Sr. Attorney would use. I've received 5 or 6 of these over the past year, maybe more and I never respond. I just hope it really is a scam. I'm very sure it is. It's always emails too, never a formal "letter". It seems ridiculous, some of the language that is used. I won't reply to them because that will just encourage them. The latest email didn't even include a phone number, just an email address ending in gmail.com.