Works great with my self-managed mail server

I host websites for clients on servers I rent in datacenters around the world. I also manage my own servers for the ancillary services needed, such as Postfix/Dovecot for mail with rspamd handling spam filtering and DKIM signing, and PowerDNS for DNS with DNSSEC.

WP Mail SMTP provided a simple way to hook into my mail server from any of the WordPress sites I host. Within 60 seconds of installing the plugin and going to the configuration screen, all of the mail sent by those WordPress sites was successfully going through my mail server directly, signed with DKIM, and passing SPF, DKIM, and DMARC checks at the destination mail server.