After considering to install SOGo I did read about the features of it and found it useful to have, so I installed the app. As I did discover the app I noticed that the promoted Multiple Mail Accounts (see below) where not configurable. But without this feature SOGo isn’t much useful for me.
https://www.sogo.nu/about.html#/features Multiple Mail Accounts
Configure all your mail accounts (IMAP) from SOGo and forget about login-in to multiple webmail services.
Is there a reason not to have this feature? And is it possible to switch it on in the configuration?
I found the configuration file under /etc/sogo/sogo.conf.
With this you can add multiple mail accounts under settings > e-mail > IMAP-accounts > new mail-account (I have it in German and did freely translate it).
I did test this feature and it seems to behave correct.