Punycode domain part of emails

[LuisaAPF]

Trying to send an email to an address like jane@döe.com fails with error:

{:error,
  {:permanent_failure, 
  '3.120.93.201',
  "501 Invalid RCPT TO address provided\r\n"}}

Using punycode to represent the domain part of the address solves this issue.

[babariviere]

Thanks for your contribution 😄 I have just made a suggestion to improve readability.