Hello,
which way do you think is the best to offer an imap client in ownCloud? Some time ago, there was a ownCloud mail app whose developers switched over to nextcloud and did not continue the development of the ownCloud mail app. The app was very buggy, and there were others like rainloop webmail which I then used – until now. The mail app is not compatible any more with ownCloud 10.1 (but can be fixed with changing the maxversion in the app code) but with ownCloud 10.2.1 its not working any more at all.
Looking on github, I found this issue: https://github.com/RainLoop/rainloop-webmail/issues/1880
So it looks like the app itself and the software behind is getting no updates at the moment. Yet another discontinued open source software project?!?
Any ideas? Leaving the cloud at version 10.0.x is not a long term solution …
I would have a look here:
In general awesome lists have their name for a reason (here is an awesome list of awesome lists).
Chose a webmail client and install it as an additional virtual host on the server, beside ownCloud. Is that what you are looking for, or do you need an integration with ownCloud?
Cheers,
Erik
Thank you very much, the lists are awesome indeed 
I already have a webmail client installed, they could also be embedded by the external link section into ownCloud but the key feature I need is the seamless ownCloud integration with automatic login into the mailbox in ownCloud. Also its desired to have multiple mailboxes integrated in one ownCloud account which can be done with rainloop.
I am really wondering about Rainloop itself, they also sell commercial licenses and the last update on the application was in July 2018, before that, Rainloop got multiple updates per year since 2014.