Greetings,
I am trying to install mailinbox in v0.21c but I failed in 
this step so I open the webmail.sh I found this URL does not exist in github
Hi 
$VERSION will be replaced with the most up to date version number, so currently "1.2.3"
referenced above is the Line 64 in /setup/webmail.sh [0]
that would look like this:
https://github.com/roundcube/roundcubemail/releases/download/1.2.3/roundcubemail-1.2.3.tar.gz
This won’t help you a lot, but the URL doesn’t seem to be the problem here 
Can you see/find any kind of Error message? I think that could make it easier to find the problem.
thank you for you help ,I am a new guy in this,I can’t find the dir of the log ,can you tell me ? I may know why this install failed CN has blocked a lot website,so some sources in this failed to laod ,so the installsion may fail in sometime