his snippet should do it. If you are denying you may want to do this in the recipient ACL after you accept postmaster and abuse addresses. Watch which servers you reject, as some legitimate senders (airlines, banks, governments) have broken rDNS on their automated senders.

Verify reverse DNS lookup of the sender's host.

deny
message Reverse DNS verification failed
!verify = reverse_host_lookup
!hosts = ${if exists{CONFDIR/local_broken_dns_whitelist}\
{CONFDIR/local_broken_dns_whitelist} {}}

I find a lot of spambots give up quickly if they don't get a connection banner quickly enough. Including the following in a connect ACL may help. Disabling pipelining catches a number of spambots that don't behave well. If the delay is too long (over 30s) some legitimate servers will also give up.

Verify reverse DNS lookup of the sender's host.

Disable piplining and delay on failure.

warn
!hosts = ${if exists{CONFDIR/local_broken_dns_whitelist}\
{CONFDIR/local_broken_dns_whitelist} {}}
!verify = reverse_host_lookup
control = no_pipelining
delay = 10s

Mobilizon is your federated organization and mobilization platform. Gather people with a convivial, ethical, and emancipating tool.

A research project I spent time working on during my master’s required me to scrape, index and rerank a largish number of websites. While Google would certainly offer better search results for most of the queries that we were interested in, they no longer offer a cheap and convenient way of creating custom search engines.

This need, along with the desire to own and manage my own data spurred me to set about finding a workflow for retrieving decent results for search queries made against a predefined list of websites. That workflow is described here, providing what I hope shall serve as a useful reference for how to go about setting up a small search engine using free and open-source tools.

Note:
• The instructions here assume that you use some UNIX-like operating system (Linux, MacOS, *BSD).
• Any Python code has only been tested using Python 3.7 (The clock is ticking).
• Any code provided is free to use under the MIT license.