A list of Inter­na­tional TLDs is avail­able on the IANA web­site. This includes the 11 IDNA i18n ‘test’ domain names as of today, and excludes .root. Use­ful for know­ing what your regex needs to match for email val­i­da­tion! Short­est 2, Longest 6, Longest inc. IDNA 18. There are no email users in the IDNA space at time of writ­ing (and, at any rate, if they are they prob­a­bly wouldn’t be par­tic­u­larly well sup­ported by legacy email and DNS sys­tems just yet!).