All email goes through a filter before it reaches your account. Most likely it is .zip which can contain viruses that can wreak havoc on your pc and the network.
This is the message you will receive:
City of Lincolnton Mail Security replaced SCAN00059310.zip with this text message. The original file contained a filtering violation and was quarantined.
Most occurances are spam that made it through the filter stage but harmful attachments have been quarantined.
If you believe your message has been quarantined by mistake please contact ITS.
For System Updates.
If you believe your message has been blocked by mistake please contact ITS by submitting a work order and requesting file be released.