For the normal envelopes that aren't oversized, do I still need some special new/modern stamp? Or can I just add different/old/normal stamps of different values to cover the postage price (0.44/0.64£)?
Also, before this change I sent a larger envelope which was oversized (A4 size envelope) but I just put ordinary stamps of different values on that one too. If say, the stamps I put on covers the new cost/postal price, will the envelope reach me? Or does this oversized need that large stamp?
Sorry but I didn't get this... Some questions here and I hope someone can answer them!

Thanks