Tell us about yourself!
It doesn't have to be 2 Gb or less, and it doesn't have to be a non-SDHC like everyone says. I've used SDHC 8Gb and so have others and they work fine. Just make sure it's formatted as fat32 and copy the files (boot.elf, Private folder) to the root of the card and not the "LetterBomb" folder. Also make sure your Wii is connected to the internet and do not use Wii to update when it asks you to after connecting to the internet. Once you put the SD in your Wii, it's a good idea to restart it and try checking your mailbox again. Try scrolling back several days then forward, past the current date, then back and forth again until you see the letterbomb envelope. I've had to do this also. Don't give up.
These people are SCAMMERS. DO NOT EMAIL!