Is it possible to buy a registered mailing envelope in advance?
We're going on honeymoon straight after our wedding and need to send our marriage cert off by registered post. Is it possible to get this organised in advance rather than trying to find a post office on the morning we fly out?
To answer your original question, yes, you can buy a registered envelope in advance. However, to post it, you must hand over the counter to obtain a receipt - you cannot post a registered envelope in a postbox. Therefore, whatever way you go about it, to register a letter, you must find a post-office which is open for business.
There is no such thing as a 'registered letter envelope'. Any envelope can be used, and the PO will just draw the X on the envelope. To send a registered letter, you just need to bring the stuff to the PO during opening hours.