The common law theory of easement by necessity will govern your situation, the elements of which are:
(1) prior common ownership
of both parcels; (2) a transfer of one of the parcels; and, (3) at the time of the transfer an easement over the property as absolutely necessary. See, e.g., Schaack v. Torsoe, 555 N.Y.S.2d 836 (2d Dept. 1990)
In order to establish it, you would have to initiate a court action involving the property over which the easement would run and receive a court order recognizing the easement. The only way to avoid court is to get the adjoining property(ies) to agree and grant a written easement.
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