I do not mean to sound glib, but I think it is a case of 'welcome to the world of spam'!
It sounds as if your email server has an effective spam filter (mine does and it is brilliant) and at least 'Mailwasher' enables you to delete said b***s before you download.
Unless our local experts think I am wrong, I have found that changing your email address will help, but it will only be a temporary respite as the spam 'trawlers' will find you again via someone's (or your) machine!