Some time ago we replaced the webmailer Roundcube with RainLoop on our servers.
Roundcube is definitely one of the best OpenSouce solutions in the field of webmail, but in the end we decided to switch to RainLoop, because this software requires far fewer resources, has numerous features “out-of-the-box” that can only be solved with Roundcube via plug-ins and can use multiple mail servers with one installation.
RainLoop and domains
In order to be able to register a mailbox with RainLoop, the corresponding domain must first be created in the admin panel. On our managed servers, this happens automatically for your mail domains, if a RainLoop installation is selected for a mail domain.
If a domain (e.g. gmail.com) is approved by the admin, the user can add his email address to this domain and can then directly switch between different mailboxes (or open them in different tabs in the browser) without having to log in to different webmailers.
Additional authentication options
Instead of logging in with the email address and password, the admin can also allow authentication via Google, Facebook or Twitter.
Contacts
In addition to storing contacts in a local database, each user can also use CardDAV, allowing them to use their contacts synchronously on numerous devices.
If you want to switch from Roundcube to RainLoop, you have to move the stored contacts manually. How to do that is described in How to transfer contacts from Roundcube to RainLoop.