My Mail Center is a browser extension where you can access multiple email inboxes quickly. However, this tool also promotes MyMailCenter.co which is a browser hijacker that will attempt to commandeer your browser search and homepage. Search results will send you to malicious websites to get money from you or infect your computer further. It may also prevent you from changing your settings back.
MyMailCenter.co is usually installed through bundled software without you knowing. Remove it immediately.