Thanks for the explanation. Yes, talk-gb is an email list - see here for some discussions on this topic:
https://duckduckgo.com/?q=site%3Ahttps%3A%2F%2Flists.openstreetmap.org%2Fpipermail%2Ftalk-gb%2F+%22post+town%22&t=osx

(More heat than light in some cases!)

Happy to accept that addr:city is for the post town. 

Checking Rob's pages here
https://osm.mathmos.net/addresses/addr-tags.html
it seems plenty of UK addresses (in OSM) also make use of addr:village. That might be better in these cases than suburb? Refreshing my memory with a quick scan of the discussions above, the village will never (or only very rarely) form part of the 'official' Royal Mail address - so it's a physical, ground-truth element, rather than referring to the RM gazetteer (which I think gets called PAF?), so I'd argue that  calling it a village rather than a suburb has informational value.