Please note, Plesk has supported the version of Mailman provided by OS vendor by default.
The Mailman 3 is shipped by default on Ubuntu 18 and Debian 10.
Please keep voting if this request is still actual for you.
AAAndré Kasper commented
please add mailman 3. mailman 2 is outdated. there are many mailman 2 issues with dmarc dkim etc. modern spam prevention often blocks mailman 2 mails. i don't understand why nobody from odin has these problems. also the interface of mailman 2 is very outdated. time to updateAndré Kasper commented
We need Mailman 3 because many Mailproviders are blocking mails from mailman 2. Please include it asap
Since Plesk Onyx you will be able to install memcache as a Docker container and configure http(s) proxy rule for it to map to your web app.
Docker and proxy rules are available in Plesk Onyx Preview already, you can try it here https://talk.plesk.com/threads/plesk-onyx-preview-and-feedback.337172/