The invention relates to a franking machine that comprises at least one print head of an inkjet printer for printing flat mail items such as letters or postcards that are inserted into or run through said franking machine. The inventive franking machine comprises a guide part that is mounted around the print head so as to project vis--vis the nozzle plane thereof. Said guide part is associated with a conveyor that conveys the mail items between itself and opposite rotating convey rollers that rotate about pins mounted transversally to the direction of conveyance. Said conveyor is provided with driving rollers that are mounted, when seen in the direction of conveyance, before and behind the print head (228). A counter-pressure roller is disposed opposite these driving rollers and exerts a pressure on a respective driving roller or on a mail item conveyed therethrough, said counter-pressure roller being reversibly liftable. The franking machine further comprises a device for servicing, cleaning and maintaining the print head. When the counter-pressure rollers (13, 15) are lowered, a service carriage (201) that is driven to be displaced transversally to the direction of conveyance of the mail items can be displaced into a service position below the print head (228).