Its the enigma plugin that comes with Roundcube but does need to be setup https://github.com/roundcube/roundcubemail/tree/634220623997a1f465e67391af48cd893706a355/plugins/enigma

Thanks for the insight. This comment made by this user on that thread was particularly interesting: https://support.cpanel.net/hc/en-us/community/posts/23150240197399/comments/23180533983767

Is it possible to keep the user guides / Help files updated - at least on the annual basis?

The v1.1 guide is too far from reality, thus almost useless and even misleading.

There is an issue between the Cloudflare DNS proxy of the webmail record (either A or CNAME) and accessing the Roundcube Inbox directly. When trying to reach a client's mailbox via https://webmail.domain.com, the page will load with SSL as it should. Whenever you try to log in, the page will try to load until it eventually gives a Cloudflare 524 timeout.

If you just set up a new mailbox account and log in for the first time, you can access the mail account configuration page, but once you try to enter the Roundcube mailbox, you will encounter the same issue as above.

On the other hand, if accessing the same mail account through WHM, which is not proxied via Cloudflare, Roundcube loads without issue. I have spent several days working with the tech team at my data center (LiquidWeb), and they are also seeing the same problem. They have ruled out conflicts except those between Cloudflare and Roundcube playing nicely.

This issue has also reached the Cloudflare forums, but a resolution has yet to be brought to light.

https://community.cloudflare.com/t/roundcube-524-a-timeout-occurred/485616/6
https://community.cloudflare.com/t/webmail-time-out/369911/4
https://community.cloudflare.com/t/mail-timeout-after-activated-cloudflare/325753
https://community.cloudflare.com/t/cpanel-webmail-after-login-does-not-load-and-gives-error-524/523763
https://community.cloudflare.com/t/cpanel-webmail-fatal-error-or-timeout-occurred-while-processing-this-directive/631322

Hopefully, someone at Roundcube can fix this issue, as the only option is to disable the proxy on the A or CNAME record. Here's a short video showing this in further detail that I also sent to my data center. https://share.peaceharbor.com/NQuAdEod

I opened a ticket on Roundcube's Github here: https://github.com/roundcube/roundcubemail/issues/9436

Fully with you. Same questions.

Many useful settings are not available (I'm using v1.6.6). The new GUI looks strange without a chance to customize it.
What if I do not like Preview Panel?

Just hope that the next update will be easier to use.