Index: app/models/mail_handler.rb
===================================================================
--- app/models/mail_handler.rb	(revision 1930)
+++ app/models/mail_handler.rb	(working copy)
@@ -39,7 +39,7 @@
   # Processes incoming emails
   def receive(email)
     @email = email
-    @user = User.find_active(:first, :conditions => {:mail => email.from.first})
+    @user = User.find_active(:first, :conditions => {:mail => email.from.first.downcase})
     unless @user
       # Unknown user => the email is ignored
       # TODO: ability to create the user's account
Index: app/models/user.rb
===================================================================
--- app/models/user.rb	(revision 1930)
+++ app/models/user.rb	(working copy)
@@ -69,6 +69,7 @@
   def before_save
     # update hashed_password if password was set
     self.hashed_password = User.hash_password(self.password) if self.password
+    self.mail.downcase!
   end
 
   def self.active