Previously, when a user entered a domain containing the Latin small letter sharp s, the web browsers automatically converted the "ß" into "ss". So domain names like "straße.de" automatically became "strasse.de". It depended on the browser type if this conversion was visible to the user in the address line. The present IDN standard, in contrast, stipulates that "ß" shall be a separate character and shall no longer be mapped to "ss". So "straße.de" and "strasse.de" now are two separate domains. As a result of the new rule, applications based on the former IDN standard are no longer compatible with the new standard. This is called lack of backwards compatibility.

As regards the user, the conversion may bring about unexpected results during a transition period because most web browsers and e-mail clients are still based on the old IDN standard. Thus, it depends on the software that is used, to which domains a user will be directed when entering a domain name that includes an "ß". While browser versions that are based on the new standard will display exactly the page the user has entered, older browser versions will always direct the user to the domain with “ss”. However, this domain may not necessarily be identical with the queried "ß"-domain, regardless whether both domains are registered by one and the same holder or not. Therefore, DENIC recommends parties interested in ß-domains to take this technical uncertainty into consideration with regards to the use of the domain.