Plesk for Linux
Why is Roundcube 1.5.0/1.6.0 not available in Plesk for CentOS 7 and Ubuntu 18.04?
Roundcube version 1.5.0 breaks support of MySQL's old versions on CentOS 7 and Ubuntu 18.04.
Hence, Plesk does not provide Roundcube 1.5.0 and 1.6.0 versions for these systems.
As an alternative to use these Roundcube versions, consider migration to fresher OSes or dist-upgrade in case of Ubuntu-based system.
For reference #PPP-54882 and #PPP-58201
If you are an engineer and you are reading it, please ask clients in your replies why do they need these Roundcube versions? and what features they miss in the current version. It is required to collect as much feedback on this matter as we can.