1&1 is a recognised internet service mainly active in the marketing, IT, and hosting sectors. Montabaur, Germany is the location of their head office.
At present, Product Development, Web Design, and Frontend Development are frequently searched for professions at 1&1. They recruit for offices in Karlsruhe, Munich, Berlin and 2 other locations within Germany. See below for a list of 60 open positions at 1&1, for instance "Infrastructure Engineer (f/m) - for our platform of the brands GMX, WEB.DE and mail.com" and "Web Developer (m/w) - for GMX and WEB.DE".
On Wikipedia, there is a well-written description of 1&1, and also worth mentioning is their social profile on Twitter. A resource not to neglect is the company's careers page with more information about open positions and career prospects.