Improved subject in oversized mail template.

app/models/channel/email_parser.rb

@@ -812,7 +812,7 @@ process unprocessable_mails (tmp/unprocessable_mail/*.eml) again
   end
 
   # Auto reply as the postmaster to oversized emails with:
-  # [ALERT] Message too large
+  # [undeliverable] Message too large
   def postmaster_response(channel, msg)
     begin
       reply_mail = compose_postmaster_reply(msg)

app/views/mailer/email_oversized/en.txt.erb

@@ -1,4 +1,4 @@
-[ALERT] Message too large
+[undeliverable] Message too large
 Dear #{mail.from_display_name},
 
 Unfortunately your email titled "#{mail.subject}" could not be delivered to one or more recipients.

spec/lib/notification_factory/mailer_spec.rb

@@ -16,7 +16,7 @@ RSpec.describe NotificationFactory::Mailer do
         mail
       end
 
-      let(:en_expected_subject) { '[ALERT] Message too large' }
+      let(:en_expected_subject) { '[undeliverable] Message too large' }
 
       let(:en_expected_body) do
         <<~BODY

spec/models/channel/email_parser_spec.rb

@@ -1014,7 +1014,7 @@ RSpec.describe Channel::EmailParser, type: :model do
     context 'for English locale (en)' do
       include_examples 'postmaster reply' do
         let(:locale) { 'en' }
-        let(:expected_subject) { '[ALERT] Message too large' }
+        let(:expected_subject) { '[undeliverable] Message too large' }
         let(:expected_body) do
           body = <<~BODY
             Dear Smith Sepp,
@@ -1074,7 +1074,7 @@ RSpec.describe Channel::EmailParser, type: :model do
     context 'for English locale (en)' do
       include_examples 'postmaster reply' do
         let(:locale) { 'en' }
-        let(:expected_subject) { '[ALERT] Message too large' }
+        let(:expected_subject) { '[undeliverable] Message too large' }
         let(:expected_body) do
           body = <<~BODY
             Dear Smith Sepp,

test/integration/email_postmaster_to_sender.rb

@@ -129,7 +129,7 @@ Oversized Email Message Body #{'#' * 120_000}
     parser = Channel::EmailParser.new
     mail = parser.parse(msg)
     assert_equal(mail[:from_email], @email_address.email)
-    assert_equal(mail[:subject], '[ALERT] Message too large')
+    assert_equal(mail[:subject], '[undeliverable] Message too large')
     assert_equal("<#{@test_id}@zammad.test.com>",
                  mail['references'],
                  'Reply\'s Referecnes header must match the send message ID')