Install and integrate Rspamd

This is the third part of our Setting up and configuring a mail server and in this part we will go through the installation and configuration of the Rspamd spam filtering system and its integration into our mail server and creating DKIM and DMARC DNS records. You may ask why we choose to go with Rspamd and not with Spamassassin. Rspamd is written in C and it is much faster then Spamassassin which is written in Perl and also Rspamd is more activlly maintained. Another reason is that Rspamd comes with a DKIM signing module so we will not have to use another software to sign our outgoing emails.