There are open access publishers and journals which send unsolicited invitation to authors to submit an article for publication. Their main purpose is to be financially profitable, but they lack any real professionalism and do not meet scholarly standards. These journals are called predatory (or parasite) journals. If you publish your article in a predatory journal you may not be able to publish it again in a serious scientific journal. Furthermore, it can harm your scientific reputation, so it is recommended to thoroughly examine the journal you wish to send your article to.