The Maine Private Ways Statute, 23 M. R. S. §§ 3101 - 3104, specifies sending "notices and other materials" by means of the United States Postal Service in §3101(2) to "owners of all the parcels benefited by the private road, ...". Postal fees may therefore be included in the assessment of owners for costs of road maintenance and, when delinquent, are rendered collectable from owners under §3104, Penalties and process.
I am not an attorney but ...
With regard to mailing costs and according to the Statute, since §3101(2) specifically requires sending by USPS and §3101(3) allows owners to decline receiving email correspondence, it would seem unacceptable to charge extra to owners who decline or discount those who accept.