I really think what they mean by a sealed letter is not a stamped one but an embossed one (when you put the letter under pressure, there will be a raised pattern) like these: http://www.embossedprinting.com/embossed-printing-pics.html
I think so because all the people form my university are given letters with this kind of seal, without stamp and not in any envelope and still they have all got PERs.
I think so because all the people form my university are given letters with this kind of seal, without stamp and not in any envelope and still they have all got PERs.