Module suppression 

Suppression list (hard-bounce blocklist).

Functions

add_suppression

add a recipient to the suppression list after a hard bounce

is_hard_bounce

detect if an SMTP error is a permanent/hard bounce (5xx)

is_suppressed

check if a recipient address is in the suppression list (hard bounce)

list_suppressions

list all suppressed addresses

remove_suppression

remove an address from the suppression list (admin override)