Abstract: An envelope opening mechanism for an inserter apparatus comprises post-like abutments (25) against which envelopes (10) are successively fed, with the hinge edge leading, over a guide surface (22) with an inclined portion (24), to initiate envelope flap opening movement by buckling of the envelope. Additionally or instead, the posts (25) can be movable downwardly to engage head portions (27) thereof with the flap portion. The envelopes are then fed in the direction of the hinge edge past an edge member (30) shaped to enter between the envelope flap and body portions and to complete the flap opening movement into alignment with the body portion for reception of insert material at an insert station (9).