How would you attract the recipients' attention, were you a spam mail writer?
I hate spam, and I am sure you do too.
In Gmail I hardly ever receive it, but in my old mail adress about one in every ten mails is spam.
They are always send directly to the bin by me, but sometimes I read the header of it before I do.
They are never that attractive that I am tempted to open them usually they are stating that “your neighbour girl wants you” or that “you want to buy blue pills for $2 a piece?”.
Most of the time spelled incorrectly as well.
So, imagine just for the sake of entertainment that you are the writer of spam mails, how would the header of your mails read?
Make it that alluring that the recipient can not even think of ditching it, but instead wants to open it to read the whole mail.