Give a pretty "from" address to the digest emails

app/mailers/user_notifications.rb

@@ -51,6 +51,7 @@ class UserNotifications < ActionMailer::Base
     # Don't send email unless there is content in it
     if @new_topics.present? || @notifications.present?
       mail to: user.email,
+           from: "#{I18n.t('user_notifications.digest.from', site_name: SiteSetting.title)} <#{SiteSetting.notification_email}>",
            subject: I18n.t('user_notifications.digest.subject_template',
                             :site_name => @site_name,
                             :date => Time.now.strftime("%m-%d-%Y"))

config/locales/server.en.yml

@@ -711,6 +711,7 @@ en:
       new_topics: "New topics:"
       unsubscribe: "This summary email is sent as a courtesy notification from %{site_link} when we haven't seen you in a while.\nIf you'd like to turn it off or change your email preferences, %{unsubscribe_link}."
       click_here: "click here"
+      from: "%{site_name} digest"
 
     private_message:
       subject_template: "[%{site_name}] %{subject_prefix}%{topic_title}"