An apparatus for conveying envelopes traveling in a travel direction in a generally upright orientation. The apparatus includes a first pair of conveyor assemblies disposed opposite one another and configured to engage lateral edges of the envelopes, and configured to move the envelopes in the travel direction. The apparatus includes a second pair of conveyor assemblies disposed opposite one another and positioned downstream of the first pair of conveyor assemblies in the travel direction, with the second pair of conveyor assemblies being configured to move the envelopes in the travel direction independently of the first pair of conveyor assemblies.