configurable maximum delivery attempts

closes #59

app/jobs/unqueue_message_job.rb

@@ -51,7 +51,7 @@ class UnqueueMessageJob < Postal::Job
             end
 
             # We might not be able to send this any more, check the attempts
-            if queued_message.attempts >= QueuedMessage::MAX_ATTEMPTS
+            if queued_message.attempts >= Postal.config.general.maximum_delivery_attempts
               details = "Maximum number of delivery attempts (#{queued_message.attempts}) has been reached."
               if queued_message.message.scope == 'incoming'
                 # Send bounceds to incoming e-mails when they are hard failed

app/models/queued_message.rb

@@ -26,8 +26,6 @@
 
 class QueuedMessage < ApplicationRecord
 
-  MAX_ATTEMPTS = 18
-
   include HasMessage
 
   belongs_to :server

app/views/help/outgoing.html.haml

@@ -18,7 +18,7 @@
         Mail servers can be enabled to send mail from any domain by the administrator.
       %li
         If a message cannot be delivered, the system will not send you a bounce message but dispatch a webhook (if you set one up).
-        If a message delivery fails but can be retried, the system will try #{QueuedMessage::MAX_ATTEMPTS} times to deliver it before giving up.
+        If a message delivery fails but can be retried, the system will try #{Postal.config.general.maximum_delivery_attempts} times to deliver it before giving up.
   .u-margin
     %h2.pageContent__subTitle Sending using SMTP
     %p.pageContent__text

config/postal.defaults.yml

@@ -11,6 +11,7 @@ web:
 general:
   use_ip_pools: false
   exception_url:
+  maximum_delivery_attempts: 18
 
 web_server:
   bind_address: 127.0.0.1