I have, in the past, received both emails and also it once happened a letter in the snail-mail post.
Written in bad English, it sort of repeats my name with words like "We found a cousin of yours..." .
Cannot remember whether any "Nigerian Princes" were involved here (as often scams mention this), but also without this, they were all scams.
The best way to find out is to google the email address or any unusual key words in the letter and more likely one will receive a web site where this is documented as a scam. If one finds that the email address seems to be legitimate, then one needs to try and find out who is behind this by further searches.
I have a story where an incomprehensible message turned out to be legitimate.
This was a personal message on one of the family tree forums written in German I think and this was before automated translations were readily available. So I could not make out the message and just put it aside and many years later, I rediscovered this and when I put it through google translate it turned out that it was a long lost son trying to make contact with his father. This father was the husband of a great aunt and the person who messaged might have been a son from his previous marriage. After my great aunt passed away, her widower became closer to my direct family, and he did not have any family from himself so I used to meet up with him when I visited England. Will call him my great uncle for simplicity. My Hungarian great uncle had actually asked me to search for any relatives of his on the Internet and I did some searches on Jewishgen etc. but could not find anything, He never talked about that he had children from a previous marriage, and if I knew that what he was after, my searching approach might have been different. Unfortunately, when I understood the message and replied to the son, my great uncle had already passed away and the person I replied to never responded, so he also was probably getting old in life.
Ma'aleh Adumim, Israel