Due to an increase of spam email, the City of Apopka has implemented a new system utilizing several methods to combat this problem.  One of the most effective and accepted ways of ensuring that a message being sent is not fraudulent, and is actually coming from where it claims to be, is Reverse DNS (RDNS) Lookups. This methodology, put simply, compares the Internet address of the server delivering the message with the designated Internet Domain Address that the server claims it is. If the Domain Name presented by the sending server can not be matched to the IP Address of the server that is actually trying at that moment to deliver the message, then the message can be considered to be spoofed.

If you are a legitimate sender, but when your system tried to deliver a message to us it was rejected, there should be an indication in your system's log file as to why. If it says something such as:
550 5.7.1 Client host rejected: cannot find your hostname, [your.ip.address.here]
(We can't give you the exact wording because it is the sending system that will interpret and identify, in its own logs, what happened).

Your IT people need to fix your HELO / EHLO statement in your sending server. This may be as simple as changing the statement in your server's configuration to use an existing DNS entry, or, you may have to work with your Internet Service Provider (ISP) to make such an entry and then enter it in to your configuration.