mail_loop – Mail Loop Detection
The mail_loop module provides automatic suppression of potential mail loops with two standard mechanisms:
-
Suppression of delivery attempts to any configured IP interfaces on the machine.
-
Suppression of messages with more than a specified number of Received headers.
The most basic configuration for the mail loop module is to suppress with a 554 code response a message with more than 20 received headers, as shown:
mail_loop "mail_loop1" { max_received_headers = 20 }
To also suppress delivery to any configured interface on the machine (interface addresses are resolved when Momentum starts), you can use:
use_ip = true
If you need to adjust the maximum number of allowed receive headers, do so as follows:
use_ip = false
max_received_headers = 32
Default value for max_received_headers is 20.
If you prefer to handle delivery suppression using policy scripts, you can disable the failing of messages by setting the return code to 250 as follows:
use_ip = true
max_received_headers = 32
code = 250
Note
Disabling trace headers will reduce the accuracy of the mail loop detection.
In this case, a loop detection will set one of two connection context variables, depending on what sort of loop was detected:
- mail_loop_header_count
-
Set to the number of received headers detected, if past the max_received_headers count.
- mail_loop_ip
-
Set to
match, if a self-connect was detected.