By Emma-Victoria Farr and Alexander Hübner
An intention to float (ITF) document could come as soon as next week, the sources said. Bloomberg first reported the news on Thursday.
On Friday, United Internet shares rose by 3% in early Frankfurt trading.
Ionos could achieve a valuation of 5 billion euros ($5.42 billion) in a stake sale, the sources said.
Ionos declined to comment.
If it goes ahead with IPO plans, Ionos could make its debut on the Frankfurt Stock Exchange by mid February, ending a lull in equity capital markets in Germany.
It would mark the first major European IPO since sports car maker Porsche in September, and would test European markets after dealmaking plunged in 2022.
In autumn last year Ionos commissioned investment banks JPMorgan, Deutsche Bank, Berenberg and BNP Paribas to prepare for the IPO.
Financial investor Warburg Pincus holds 24.9% of Ionos and could initiate its exit with the IPO, the sources said. Warburg Pincus was not immediately available to comment.
($1 = 0.9229 euros)
(Reporting by Emma-Victoria Farr, Alexander Huebner, Hakan ErsenWriting by Miranda Murray Editing by Rachel More and Mark Potter)
