Redmine

Non-ASCII characters cannot be used in an email address.
This issue can be fixed by the following patch.

Index: app/models/email_address.rb
===================================================================
--- app/models/email_address.rb    (revision 16179)
+++ app/models/email_address.rb    (working copy)
@@ -26,7 +26,7 @@
   after_destroy :destroy_tokens, :deliver_security_notification_destroy

   validates_presence_of :address
-  validates_format_of :address, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i, :allow_blank => true
+  validates_format_of :address, :with => /\A([[:ascii:]&&[^@\s]]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i, :allow_blank => true
   validates_length_of :address, :maximum => User::MAIL_LENGTH_LIMIT, :allow_nil => true
   validates_uniqueness_of :address, :case_sensitive => false,
     :if => Proc.new {|email| email.address_changed? && email.address.present?}

Go MAEDA wrote:

Non-ASCII characters cannot be used in an email address.

Yes, they can. More and more clients and server support that.
We cannot simply disallow them in Redmine.

Redmine now supports internationalized domain names as of r22667.

Suppose you mistakenly enter user@straße.example instead of user@strasse.example as your email address. In that case, Redmine converts the email address to its ASCII representation user@xn--strae-oqa.example after clicking the "Save" button and displays the converted one on the screen. Therefore you will immediately notice there is some "problem" with the email address you entered.

1. Entering email address contains a non-ASCII character

2. The ASCII representation of the email address is displayed after saving