Though I do think it better to present the Japanese email as ニチン@データメール.コム rather than ニチン／データメール。コム

From the graphic I think it is fullwidth slash (as opposed to standard ASCII slash) and the ideographic full stop that is being displayed. I do vaguely recollect that there are/were some issues with some Japanese Input Methods whereby @ would by default be mapped to ／ or some such unexpected mapping.