Lottery winners..?

In the last 3 weeks I have gotten email from 4 different lottery companies telling me I am a winner. each lottery is different and each wants me to pay ins. and postage to have my check delivered. also each lottery for some unkbnown reason is based in canada . has this happend to anyone else? of course I haven't sent any money for delivery or what ever. how do I know that all of these are scams? Is there any real ones? two of the lottery's are from well known companys.when ever I reply and ask questions I am never answered, They reply with another letter asking for money for delivery.any suggestions?