From Longman Dictionary of Contemporary Englishpillar boxˈpillar box noun 
[countable] British English old-fashionedTCM a large red tube-shaped box for posting letters that stands on streets in Britain SYN postbox, → letterbox
[countable] British English old-fashionedTCM a large red tube-shaped box for posting letters that stands on streets in Britain SYN postbox, → letterboxExamples from the Corpus
pillar box• How my heart leaped to see a red pillar box once more, on the other side of the compound!• Mrs Southworth from the Hall was at the pillar box, posting a letter. 