A method, system and article for producing an envelope having improved seal integrity. A method includes the steps of: disposing at least one material at the interface of the adhesive seal between the flap and the body portion of the envelope, which material radiates thermal energy when combined with an activating agent. The envelope is then sealed by closing the flap onto the body portion of the envelope and combining the material with the activating agent at the sealing interface so as to change the thermal energy radiated therefrom. The seal is then inspected to determine whether the thermal energy radiated from the activated material has changed thereby confirming that a seal has been produced between the flap and body portion of the envelope. The system and article are directed to the various modules of a mailpiece fabrication system employed to produce the mailpiece including an inspection module for confirming that a seal has been formed.