Hi, our block of flats were built in the 1980’s and have letterbox’s in the door. We have no information on these doors so I just wanted to know would we need the doors replaced as I heard unless the manufacturer says you can, fire doors cannot be drilled through. As we have no evidence how can we be sure these doors will perform in a fire?

Some fire doors can have apertures for fire resistant and smoke restricting letter plates.  My advice would be to engage a competent & experienced fire door inspector to verify whether or not the doors are suitable in terms of their fire and smoke performance, as flat entrance doors.