I have the same issue. Fighting with it the whole day.
It looks this one is the same Someone help me fix this problem ive been Stuck for days in it
Something is definitely broken in the installer. I assumed maybe Hetzner (hoster) ha some modifications in Ubuntu image. Switched to the Digital Ocean. The problem stays.
The problem is that the bin/ dir is missing:
$ ls -lha /usr/local/lib/mailinabox/env
total 24K
drwxr-xr-x 4 root root 4.0K Nov 28 00:28 .
drwxr-xr-x 3 root root 4.0K Nov 28 00:28 …
-rw-r–r-- 1 root root 40 Nov 28 00:28 .gitignore
drwxr-xr-x 3 root root 4.0K Nov 28 00:28 lib
drwxr-xr-x 4 root root 4.0K Nov 28 00:28 local
-rw-r–r-- 1 root root 207 Nov 28 00:28 pyvenv.cfg
I created the symb link to local/bin. Setup went forward but at the step of entering email it stuck.
It says the email_validator module is not found (But it is installed in both systemwide and virtual env).
Not sure what else can be done.