The RL781DT was not specifically tested with postage machines but did test well with direct thermal Zebra printer models. This product has a 1" core and an outer diameter of 4" so you will want to make sure this meets your printer's requirements. Please feel free to visit the link below to have free samples mailed to you for testing. https://www.onlinelabels.com/samples If you’d like assistance in finding the right product for your printer, please contact our Customer Support Team at 888-575-2235.