Roundcube 524 A timeout occurred

[fritex]

@jure

but when I click on Roundcube and start opening

Where exactly do you click?
On the logo, or login button or somewhere else?

Does any error appear in the Console of the Developer Tools (F12) at your Web browser?

May I ask what troubleshooting steps have you already tried regarding the 524 error you’re getting for your Website from the article below?

Community Tip - Fixing Error 524: A timeout occurred

Error Try the suggestions in this Community Tip to help you fix Error 524: A timeout occurred. Background Error 524 error indicates that Cloudflare made a successful TCP connection to the origin web server, but the origin did not reply with an HTTP response before the connection timed out. Typically, Cloudflare waits 100 seconds for an HTTP response. If the origin doesn’t respond in that time, Cloudflare closes the connection and you’ll see “Error 524: A timeout occurred”. [PRO UP SELL] Qui…

Before moving to Cloudflare, was your Website working over HTTPS connection?
You could determine this by:

1. Use the “Pause Cloudflare on Site” option from the Overview tab for your domain at dash.cloudflare.com .
2. The link is in the lower right corner of that page.
3. Give it five minutes to take effect, then make sure site is working as expected with HTTPS without any error
4. Check with your hosting provider / cPanel AutoSSL / Let’s Encrypt / Certbot / ACME and renew it in case if needed
5. Only then, when your website responds over HTTPS, you should un-pause Cloudflare and double-check your SSL/TLS setting to make sure it’s Full (Strict).

What port are you using to access your Webmail?

May I ask what SSL option have you got selected under the SSL/TLS tab at Cloudflare dashboard for your domain ( Flexible, Full, Full Strict … )?