Are german umlauts (ä, ö, ü) and the sz-character (ß) valid in the local part of an email-address?
For example take this email-address: björn.nußbaum@trouble.org
RFC 5322 quite clearly says, that umlauts (and other international characters) aren't allowed. If I take a look at chapter 3.4.1, there's the following regarding the local part:
local-part = dot-atom / quoted-string / obs-local-part
So what means dot-atom? It's described in chapter 3.2.3: Well, long story short: Printable US-ASCII characters not including specials
So in the whole RFC 5322 I can't see anything regarding international characters. Or is RFC 5322 already obsolete? (RFC 822 -> RFC 2822 -> RFC 5322)
Update: The important point for me is: What's the current standard? International characters allowed or not? RFC 5322 is marked as DRAFT STANDARD. So I think that's the most recent source to rely on, isn't it?
Efran mentioned, that RFC 5336 allows international characters. But RFC 5336 is marked as EXPERIMENTAL, so that's not interesting for me.
Yes, they are valid characters as long as the mail exchanger responsible for the email address supports the UTF8SMTP extension, discussed in RFC 5336. Beware that just a small portion of the mail exchangers out there supports internationalized email addresses.
Both our email validation component for Microsoft .NET and our REST email validation service, for example, allow UTF8 characters in the local part of an email address but will mark it as invalid if its related mail exchanger does not support the aforementioned extension.
https://tools.ietf.org/html/rfc5322#section-3.4.1 is your latest standards track reference. Generally it is not advisable to use characters which require quoting due to the outrageously high amount of standards unconformant MTAs out there. Such email are bound to get lost in the long run.
As a friendly advice this table is pretty useful too: http://www.remote.org/jochen/mail/info/chars.html
It looks like rfc6531 replaces 5336 and it is "PROPOSED STANDARD" https://tools.ietf.org/html/rfc6531
来源：https://stackoverflow.com/questions/15121359/are-international-characters-e-g-umlaut-characters-valid-in-the-local-part-of