I am currently getting:
Unable to connect to the database!
Please contact your server-administrator.
How can I diagnose this? Am I the only one experiencing this issue?
Thanks.
I can confirm a clean install of tag V0.21 -> tag V0.22 (and master) does work. I do not get an error about connecting to the database.
You might try and remove the carddav plugin (Line 19) $config[‘plugins’] from your /usr/local/lib/roundcubemail/config/config.ini.php and see if that connects. Carddav will not be enabled, but you should be able to access mail again.
You can also try and re-run the setup ./setup/start.sh
Confirmed - this broke my install too 
The fix about removing the cardav plugin does let roundcube work again.
Same here @wuxmedia
Now working on this side. Lately each time I upgrade mailinabox, I have a problem.
Bummer. This is my first upgrade.
I’m not migrating my users again 
You can also check that you have a address book created in owncloud/nextcloud. If you upgraded from an early version of MiaB it may not have created one.
- Login into owncloud/nextcloud. (
https://yourdomain.com/cloud) - Select the Contacts from top left menu
- Select “Settings” from the bottom left
- If you don’t see “Contacts” or any other names, create one.
- Try and login back into /mail with carddav enabled again.
Thanks Elser,
That also works nicely.
Good if one doesn’t fancy getting into editing config files.(I don’t care - it’s my day job 
)
TBH I’d forgotten I have a cloudthing now!
“You might try and remove the carddav plugin (Line 19) $config[‘plugins’] from your /usr/local/lib/roundcubemail/config/config.ini.php and see if that connects. Carddav will not be enabled, but you should be able to access mail again.”
Just ran into this problem. This let me get back into my email after upgrading.