More detailed email rejection responses

app/jobs/scheduled/poll_mailbox.rb

@@ -22,23 +22,36 @@ module Jobs
       begin
         mail_string = mail.pop
         Email::Receiver.new(mail_string).process
-      rescue Email::Receiver::UserNotSufficientTrustLevelError
+      rescue => e
         # inform the user about the rejection
         message = Mail::Message.new(mail_string)
-        client_message = RejectionMailer.send_trust_level(message.from, message.body)
-        Email::Sender.new(client_message, :email_reject_trust_level).send
-      rescue Email::Receiver::ProcessingError => e
-        Rails.logger.error e
-        message = Mail::Message.new(mail_string)
-        client_message = RejectionMailer.send_rejection(message.from, message.body, e.message)
+        message_template = nil
+        case e
+          when Email::Receiver::UserNotSufficientTrustLevelError
+            message_template = :email_reject_trust_level
+          when Email::Receiver::UserNotFoundError
+            message_template = :email_reject_no_account
+          when Email::Receiver::EmptyEmailError
+            message_template = :email_reject_empty
+          when Email::Receiver::EmailUnparsableError
+            message_template = :email_reject_parsing
+          when ActiveRecord::Rollback
+            message_template = :email_reject_post_error
+          else
+            nil
+        end
 
-        # inform admins about the error
-        data = { limit_once_per: false, message_params: { source: mail, error: e }}
-        GroupMessage.create(Group[:admins].name, :email_error_notification, data)
-      rescue StandardError => e
-        # inform admins about the error
-        data = { limit_once_per: false, message_params: { source: mail, error: e }}
-        GroupMessage.create(Group[:admins].name, :email_error_notification, data)
+        if message_template
+          # Send message to the user
+          client_message = RejectionMailer.send_rejection(message.from, message.body, message_template.to_s, "#{e.message}\n\n#{e.backtrace.join("\n")}")
+          Email::Sender.new(client_message, message_template).send
+        else
+          Rails.logger.error e
+
+          # If not known type, inform admins about the error
+          data = { limit_once_per: false, message_params: { from: message.from, source: message.body, error: "#{e.message}\n\n#{e.backtrace.join("\n")}" }}
+          GroupMessage.create(Group[:admins].name, :email_error_notification, data)
+        end
       ensure
         mail.delete
       end

app/mailers/rejection_mailer.rb

@@ -3,11 +3,11 @@ require_dependency 'email/message_builder'
 class RejectionMailer < ActionMailer::Base
   include Email::BuildEmailHelper
 
-  def send_rejection(from, body, error)
-    build_email(from, template: 'email_error_notification', error: "#{error.message}\n\n#{error.backtrace.join("\n")}", source: body)
+  def send_rejection(from, body, template, error)
+    build_email(from, template: template, error: error, source: body)
   end
 
-  def send_trust_level(from, body)
+  def send_trust_level(from, template)
     build_email(from, template: 'email_reject_trust_level')
   end
 end

config/locales/server.en.yml

@@ -1302,9 +1302,13 @@ en:
       text_body_template: |
         This is an automated message.
 
-        Parsing an incoming email failed. Please review the following Error:
+        Parsing an incoming email from `%{from}` failed. Please review the following Error:
 
-        `%{error}`
+        ---
+
+        %{error}
+
+        ---
 
         The original message follows.
 
@@ -1313,12 +1317,40 @@ en:
         %{source}
 
     email_reject_trust_level:
-      subject_template: "Message rejected"
+      subject_template: "Message rejected: Insufficient Trust Level"
       text_body_template: |
         The message you've send to %{to} was rejected by the system.
 
         You do not have the required trust to post new topics to this email address.
 
+    email_reject_no_account:
+      subject_template: "Message rejected: No Account"
+      text_body_template: |
+        The message you've send to %{to} was rejected by the system.
+
+        You do not have an account on the forum with this email address.
+
+    email_reject_empty:
+      subject_template: "Message rejected: No Content"
+      text_body_template: |
+        The message you've send to %{to} was rejected by the system.
+
+        There was no recognized content in the email.
+
+    email_reject_parsing:
+      subject_template: "Message rejected: Unparsable"
+      text_body_template: |
+        The message you've send to %{to} was rejected by the system.
+
+        The encoding was unknown or not supported. Try sending in UTF-8 plain text.
+
+    email_reject_post_error:
+      subject_template: "Message rejected: Posting error"
+      text_body_template: |
+        The message you've send to %{to} was rejected by the system.
+
+        The Markdown could not be processed.
+
     too_many_spam_flags:
       subject_template: "New account blocked"
       text_body_template: |