ZOHO on US Government blacklist? ZOHO doesn't care?

ZOHO on US Government blacklist? ZOHO doesn't care?

At the bottom of this post is a list of discussion threads by people who - like me - can't send email to United States Department of Defense email addresses from ZOHO's servers. 

The most common problem seems to be a ResponseCode 421, Host not reachable error, which suggests that ZOHO's servers are on a blacklist.

The US Government does not blacklist companies for no reason (to the contrary, it does business with some pretty shady organizations). The fact that ZOHO's servers are apparently blacklisted is a big deal, and suggests that ZOHO is allowing spammers to use the network. 

The existence of so many topics on this point - and its non-resolution - shows that ZOHO doesn't care.