A system for application of liquid for moistening adhesive on envelope flaps as part of an automated mail production process, the system comprising: a moistening brush (1; 20) positioned above a location at which open envelope flaps will be transported so that an interior side of the flaps, having adhesive thereon, comes into contact with a lower end of the moistening brush (1; 20), thereby transferring moisture from the moistening brush (1; 20) to the interior side of the flaps; a liquid supply coupled to the moistening brush (1; 20) providing a flow of liquid to keep the moistening brush (1; 20) wet as moisture is transferred to the envelope flaps, the liquid supply including a controlled pump for regulating a rate at which liquid is supplied to the moistening brush (1; 20); a controller in operative communication with the controlled pump, characterised in that the controller is configured to: automatically determine, for each envelope flap to be moistened, a dose comprising a selected quantity of liquid as a function of physical dimensions of the envelope flap indicative of the area of the envelope flap, the dose being adequate for sealing the envelope, but limited such that there is only a nominal amount of excess liquid; and regulate a flow of liquid to the brush (1; 20) such that the determined dose is provided for each envelope flap that it moistens so that moisture is maintained on the brush (1; 20). a moistening brush (1; 20) positioned above a location at which open envelope flaps will be transported so that an interior side of the flaps, having adhesive thereon, comes into contact with a lower end of the moistening brush (1; 20), thereby transferring moisture from the moistening brush (1; 20) to the interior side of the flaps; a liquid supply coupled to the moistening brush (1; 20) providing a flow of liquid to keep the moistening brush (1; 20) wet as moisture is transferred to the envelope flaps, the liquid supply including a controlled pump for regulating a rate at which liquid is supplied to the moistening brush (1; 20); a controller in operative communication with the controlled pump, characterised in that the controller is configured to: automatically determine, for each envelope flap to be moistened, a dose comprising a selected quantity of liquid as a function of physical dimensions of the envelope flap indicative of the area of the envelope flap, the dose being adequate for sealing the envelope, but limited such that there is only a nominal amount of excess liquid; and regulate a flow of liquid to the brush (1; 20) such that the determined dose is provided for each envelope flap that it moistens so that moisture is maintained on the brush (1; 20). automatically determine, for each envelope flap to be moistened, a dose comprising a selected quantity of liquid as a function of physical dimensions of the envelope flap indicative of the area of the envelope flap, the dose being adequate for sealing the envelope, but limited such that there is only a nominal amount of excess liquid; and regulate a flow of liquid to the brush (1; 20) such that the determined dose is provided for each envelope flap that it moistens so that moisture is maintained on the brush (1; 20).