Test if your SMTP-server is modern

Can your mail server send to jörg at übungsgelän.de ?

gmail can. It means, it can resolve DNS via IPv6, deliver via IPv6 MX, and handle Unicode in both domain-names and user-names.

if your mailer cannot, then try
  1. joerg at 4.übungsgelän.de
  2. joerg at xn--bungsgeln-22a9w.de
  3. joerg at 4.xn--bungsgeln-22a9w.de
  4. joerg at only6.zq1.de
  5. jörg at zq1.de

Why does this matter?

Since IPv4 addresses are depleted, not everyone can host his DNS or mail-server on a v4 address, but IPv6 addresses are plenty and available.

UTF-8 is the standard to represent any relevant characters on earth (even Klingon). Mail servers should not force people into an ASCII-only world.