MailCleaner before 28d913e has default values of ssh_host_dsa_key, ssh_host_rsa_key, and ssh_host_ed25519_key that persist after installation.
https://www.mailcleaner.net/infobox/mc-info-box.php
https://github.com/MailCleaner/MailCleaner/wiki/Watchdogs#host_keys
https://github.com/MailCleaner/MailCleaner/commit/28d913eaa044b689eb114f72ebe92d48cb4aaca7