Vanity publishers are taking advantage of the open access movement. These publishers scour professional email lists, soliciting article submissions for a cost. They could have false-front or non-existent peer review processes.
If you receive an email asking you to publish, make sure you research that publisher, and verify that their name does not appear on Beall’s List of Predatory Publishers.
Make sure to also take a look at Beall’s Criteria for Determining Predatory Open-Access Publishers (2nd edition) for many useful tips.