I can't believe that I have gone 30 years without knowing the answer to this but - I have an A4 letter to post. It has a large first class stamp on it and is not heavy as it only has a couple of sheets of paper inside. Can I or can I not put it through the postbox? I need to post it today and it will be a huge PITA if I need to go to the post office just to do this, given it already has the correct stamp. The dimensions given on the Royal Mail website (here: personal.help.royalmail.com/app/answers/detail/a_id/138/~/where-can-i-post-my-letter%2Fparcel%3F) seem enormous and I worry that they aren't right!
It doesn't need to be tracked or anything.
