Add IP-based SMTP authentication (#1149)

lib/postal/smtp_server/client.rb

@@ -312,8 +312,18 @@ module Postal
           end
 
         else
-          # This is unaccepted mail
-          '530 Authentication required'
+          # User is trying to relay but is not authenticated. Try to authenticate by IP address
+          @credential = Credential.where(:type => 'SMTP-IP').all.sort_by { |c| c.ipaddr&.prefix || 0 }.reverse.find do |credential|
+            credential.ipaddr.include?(@ip_address)
+          end
+
+          if @credential
+            # Retry with credential
+            @credential.use
+            rcpt_to(data)
+          else
+            '530 Authentication required'
+          end
         end
       end