How can I uninstall acymailing 7 totally and keep only acymailing 5, I cannot find an easy way
Go to Joomla->Extensions->Manage->Manage and search for Acymailing. Look at the version numbers and uninstall version 7.
That's fine but the tables acym_% are still in de DB. And when I delete them manually, an error "1146 Table 'u87439p82309_temp.#__acym_configuration' doesn't exist" is the result and the backend of the site doesn't start up anymore.
Please raise a support ticket for this (https://www.acymailing.com/support/) and include login credentials for your backend so we can have a look at it.
I could raise a ticket but the backend doesn't start up anymore. Before I do this, the reason why I want to remove V7 is that I can't find how to address CB fields in a mail. I presume this is a feature that isn't there any more. Is there a planning when to implement this again?
Try deleting this folder on your server: /administrator/components/com_acym After that you should be able to login to your backend again.
There's an add-on available for Community Builder. It's documented here: https://docs.acymailing.com/addons/joomla-add-ons/community-builder
Nice to hear that there is an add-on available. But I can't find a download link for it.
Everything is documented: https://docs.acymailing.com/main-pages/add-ons