7 cards where the illustration contains “envelope”

Dimir Informant (Guilds of Ravnica #36)
Dispatch Dispensary (Unstable #176)
Furtive Courier (Murders at Karlov Manor #59)
Imperial Seal (Double Masters 2022 #79)
Insufferable Syphon (Unstable #191)
Patriar's Seal (Commander Legends: Battle for Baldur's Gate #332)
Wedding Invitation (Innistrad: Double Feature #527)

Though this query has ended, its relics still slumber in New Argive.