It could may be the 'x_frame_options' or 'session_samesite' config options you need to adjust. Details of the issue would help, what is reported in the browser (and browser console) or in the Roundcube error log?

iframes are often messy when it comes to browser security, the more info you can provide the more likely someone has some advice for you.

This seems to be a common question but I can't quite nail the answer. I have an i-frame on my site and it displays the domain's Roundcube webmail. That's all fine, but it won't allow the user to insert their password, rejecting the action as invalid.

Any easy fixes? Many thanks.

I have a installation of Roundcube 1.6.6 behind a Cloudflare proxy and it works fine. I'm guessing it is aa issue with the cPanel customizations or web server config that is causing the problem.

I have 8 dedicated servers, and all the websites hosted on them are experiencing the same issue. Two of these servers were installed just 4 days ago without any modifications to cPanel. I only installed the system, cPanel, and transferred the websites to them without NS or anything only change DNS from cloudflare, yet the same problem.

But I followed the steps I mentioned above and solved the issue on all of my servers.
It's a temporary solution until roundcube and cpanel fix this issue.

Just so you know, when the issue was present, I created a subdomain in Cloudflare for another domain and linked the IP address of the server experiencing the problem. This allowed the webmail to work for me.

Example:
The problem was with this domain, "webmail.server1.com."
I added a subdomain on the domain "test.server2.com" and linked the IP address of server1 to the subdomain "test.server2."
This made the webmail work for me.

Alright, I've solved the problem, and indeed it was caused by Roundcube. I performed a downgrade of Roundcube from version 1.6.6 to 1.6.0, and the issue was resolved.

Here's how I did it:
I navigated to the following path:

/usr/local/cpanel/base/3rdparty
and renamed the Roundcube folder to roundcube_bak. Then, I pulled files from another website for Roundcube version 1.6.0 and uploaded them to the same path on my server.

I use the Larry interface for my business email and it changed today to elastic is there any way to change this back to Larry??