FEATURE: Allow posting via email to read-only mailing list mirror category

lib/email/receiver.rb

@@ -451,7 +451,7 @@ module Email
         category = destination[:obj]
 
         raise StrangersNotAllowedError    if user.staged? && !category.email_in_allow_strangers
-        raise InsufficientTrustLevelError if !user.has_trust_level?(SiteSetting.email_in_min_trust)
+        raise InsufficientTrustLevelError if !user.has_trust_level?(SiteSetting.email_in_min_trust) && !sent_to_mailinglist_mirror?
 
         create_topic(user: user,
                      raw: body,
@@ -753,6 +753,11 @@ module Email
         options[:raw] << Email::Receiver.elided_html(options[:elided])
       end
 
+      if sent_to_mailinglist_mirror?
+        options[:skip_validations] = true
+        options[:skip_guardian] = true
+      end
+
       user = options.delete(:user)
       result = NewPostManager.new(user, options).perform
 

lib/post_creator.rb

@@ -130,7 +130,7 @@ class PostCreator
       return false unless skip_validations? || validate_child(topic_creator)
     else
       @topic = Topic.find_by(id: @opts[:topic_id])
-      if (@topic.blank? || !guardian.can_create?(Post, @topic))
+      unless @topic.present? && (@opts[:skip_guardian] || guardian.can_create?(Post, @topic))
         errors[:base] << I18n.t(:topic_not_found)
         return false
       end

spec/components/email/receiver_spec.rb

@@ -799,11 +799,11 @@ describe Email::Receiver do
   end
 
   context "mailing list mirror" do
+    let!(:category) { Fabricate(:mailinglist_mirror_category) }
+
     before do
       SiteSetting.block_auto_generated_emails = true
       SiteSetting.find_related_post_with_key = true
-
-      Fabricate(:mailinglist_mirror_category)
     end
 
     it "should allow creating topic even when email is autogenerated" do
@@ -817,5 +817,26 @@ describe Email::Receiver do
 
       expect { process(:mailinglist_reply) }.to change { topic.posts.count }
     end
+
+    context "read-only category" do
+      before do
+        category.set_permissions(everyone: :readonly)
+        category.save
+
+        Fabricate(:user, email: "alice@foo.com")
+        Fabricate(:user, email: "bob@bar.com")
+      end
+
+      it "should allow creating topic within read-only category" do
+        expect { process(:mailinglist) }.to change { Topic.count }
+      end
+
+      it "should allow replying within read-only category" do
+        process(:mailinglist)
+        topic = Topic.last
+
+        expect { process(:mailinglist_reply) }.to change { topic.posts.count }
+      end
+    end
   end
 end