Adds the source of the current message to the blacklist for timeout seconds. If timeout is missing or 0 it uses the default blacklist timeout (dst_blacklist_expire).

...
if (src_ip==10.0.0.0/9)
    blst_add(30); # 30 s
else
    blst_add();  # use default blacklist timeout
...

Adds the source of the current message to the blacklist for the time interval specified in the Retry-After header. If the Retry-After header is missing, it will fail (returns false). If the Retry-After value is less then min, then min seconds will be used instead. If the Retry-After value is greater then max, then max seconds will be used instead.

...
# on_reply route
if (msg_status==503){ # blacklist 503 source for Retry-After seconds
    if (! blst_add_retry_after(30, 3600))
        blst_add(60); # if no retry_after header add it for 60s
}
...

Removes the source of the current message from the blacklist. If the address is not present in the blacklist at the time of the call it returns false.

...
    blst_del();
...

Returns true if the source of the current message is blacklisted.

...
    if (blst_is_blacklisted()){
        log("message from a blacklisted source");
        drop;
   }
...