You are permitted to list a property in multiple towns if 1.) it is physically located in more than one town, or 2.) if the street on which it located can only be entered from an adjoining town.
Below is the section of the SmartMLS Rules & Regulations that goes into more detail regarding this process:
Section 4.11 Listing Properties in Multiple Towns. No property shall be listed in more than one town, unless: i) it is physically located in more than one town, or; ii) the street on which the property is located can only be entered from an adjoining town. If a property meets one or both of the above criteria, the Listing Broker may elect to place the property Listing in each appropriate town provided: A. the Listing broker must immediately notify the Service, in writing, of the fact that the property has been listed in more than one town. (Printed copies of the Listing as it appears in each town must be included with the notification.) B. The first line in the “Remarks” section of the adjoining town Listing must clearly indicate the town(s) in which the property is physically located and the municipal school system(s) serving the property. C. The Listing Broker must notify the Service, in writing, as soon as the property is sold; the Listing expires or is cancelled. Upon such notification, or if a property that fails to meet the criteria listed above is listed in an adjoining town, the Service shall remove the adjoining town Listing. Any broker placing a Listing in violation of this section shall be fined in accordance with these Rules and Regulations.