The Daily Mail's head of trading, Jon O'Donnell, is moving across to become deputy advertising director at the Evening Standard, reporting to his former boss Simon Davies. O'Donnell has worked at the group's Manchester and London offices for about 10 years.
Mays, former press director at ZenithOptimedia, joined The Mail on Sunday in the client sales role in November 2005.
He reported to the newspaper's managing director Stephen Miron, who left recently to take on the managing director's role at Global Radio. It is not known if Mays has a job to go to.
Other departures from the group include Yas Leadbeater, senior display executive, and Vanessa Jeffrey, head of new business at The Mail on Sunday, as parent group Daily Mail & General Trust (DMGT) looks to better compete in the marketplace by merging the sales operations of the Daily Mail and The Mail on Sunday.
Media Week last week reported that DMGT had handed new roles to The Mail on Sunday ad director Simon Davies and Evening Standard and London Lite ad chief Rosemary Gorman.
Davies has become ad director of the Evening Standard and London Lite, reporting to the paper's managing director Andrew Mullins and London Lite managing director Steve Auckland.
Davies replaces Gorman, who has moved to become deputy ad director at Mail Newspapers.
Gorman now reports to the newly appointed ad director, John Teal.