FIX: Handle incoming emails without email address in From header (#5177)

spec/components/email/receiver_spec.rb

@@ -37,6 +37,10 @@ describe Email::Receiver do
     expect { process(:no_body) }.to raise_error(Email::Receiver::NoBodyDetectedError)
   end
 
+  it "raises a NoSenderDetectedError when the From header is missing" do
+    expect { process(:no_from) }.to raise_error(Email::Receiver::NoSenderDetectedError)
+  end
+
   it "raises an InactiveUserError when the sender is inactive" do
     Fabricate(:user, email: "inactive@bar.com", active: false)
     expect { process(:inactive_sender) }.to raise_error(Email::Receiver::InactiveUserError)
@@ -229,10 +233,14 @@ describe Email::Receiver do
     end
 
     it "handles invalid from header" do
-      expect { process(:invalid_from) }.to change { topic.posts.count }
+      expect { process(:invalid_from_1) }.to change { topic.posts.count }
       expect(topic.posts.last.raw).to eq("This email was sent with an invalid from header field.")
     end
 
+    it "raises a NoSenderDetectedError when the From header doesn't contain an email address" do
+      expect { process(:invalid_from_2) }.to raise_error(Email::Receiver::NoSenderDetectedError)
+    end
+
     it "doesn't raise an AutoGeneratedEmailError when the mail is auto generated but is whitelisted" do
       SiteSetting.auto_generated_whitelist = "foo@bar.com|discourse@bar.com"
       expect { process(:auto_generated_whitelisted) }.to change { topic.posts.count }