I have an idea of a feature that could be added to OpenStreetMap, it would be useful to have this feature. Where can I make suggestions to OpenStreetMap?
Hi and welcome to OSM
Here you are at the right place! 
Thank you!
Well here is my suggestion:
Something that is useful on other software like Google Maps is the ability to have postcode (I’m from the UK but I believe in the US these are called zip codes) areas. When you search a code and the area in Google maps, it outlines the area in red. I tested with a US zip code and it does so in the US also, not just the UK. This is my suggestion!
OSM has postcode centroids in the UK which are open data.
A postcode applies to a maximum of about 40 addresses but address/postcode data is not open.
To draw postcode boundaries, where we can derived them, would involve drawing the boundaries of every property and grouping them. That would be a lot of work for volunteers.
The existing centroid search will usually get you pretty close in built up areas.
Cheers Phil
and welcome to the forum! Your question has been answered already but just a hint fyi: It does not make much sense to put the same question in different categories of the forum at the same time.
Choose one categorie and open you topic there and you will surely get an answer. If you chose the wrong category, another user will help to shift it to the correct place.