From 1568 Montelupi was postmaster general of the Polish Royal Post (succeeding Pietro Maffon), running one public service to Vilnius (in three weeks) and another to Vienna and Venice (in ten days) [REF].
At Sebastiano's death the postmastership also passed to his nephew Valerio, and in time to Valerio's descendants, the last postmaster of the dynasty being Carlo Montelupi de Mari (Karol Montelupi, died 1662) [REF].