They are usually ads for sex enhancement products
If you do not know who they are from or they have no content marked- simply delete unread.
Actually as these scammers are up to all sorts of trick to circumvent our protection methods it its best to remove your E-mail programs from the start group.
Look at your mail on line in your ISP,s web mail section, delete it what you don't like the look of there by sending it to the 'blacklist' or block box
then when only the genuine stuff remains come back to your desk top and run the E-mail program.
Then only the stuff you approve of will come in.
Once it is in close the program so that no more uninvited comes down the wire.
All long winded but is the only sure way of stopping the stuff