Hey together! I made a Text-Tutorial how to setup a Webmail + Roundcube on your AA-Panel Web-Server.

What you need / configuration:

NGINX
MySQL
Webmail / MailSys4 (Blue/White Icon)
Redis
1-Click-Deployment Addon
PhPMyAdmin
PHP (at least 7.4)

Setup Process

Go to the App-Store and make sure all Apps you need are on the Home Display(Mail-Server, 1-Click-Deploy, Redis)
Open Redis > Performance tuning > Enter a random password at the "requirepass" field > Click on Save > Exit Redis
Click on Mail-Server > You get a message "Mail Server is not installed, is it installed?", hit "Confirm" > (Everything should be green / show ready) > Hit Submit > The System will now install the Mail-Server, this can take some time.

Now go to your DNS Host like Cloudflare. (Do not Tunnel the Records!)
First we add 3 "A" Records:

A | @ | YourServerIpAdress
A | mail | YourServerIpAdress
A | webmail | YourServerIpAdress

Now our Web-Mail Server is ready. We can add our "Domain(s)" we wanna use for our E-Mail now.
Hit "Add Domain" in the Webmail > In the first Line Enter your Domain, in the second enter "mail.yourdomain.tld".
(You might get an Error here that says "A record [mail.yourdomain.tld] does not belong to the domain name" - This might happen if your DNS is not up to date. Please wait a few hours till the DNS is updated).
Hit "Submit" > Then the Server will verify your Data. Please be patient. It might take a while.
Now you see a Panel showing you a lot of Records > Click on a "Not Set" Record. > The System then shows you a Pop-Up with the Instructions. Follow them and add the Records to your DNS (a.E. Cloudflare).
After you added all the Records hit "Already set.." and wait till the Server checks all Records.

Now we add an SSL Form to our Domain > Hit "Add SSL" > DNS Verification > Manual Resolution > Select your Domain > Hit Apply > Follow the Instructions of the SSL-Bot and Apply.
If the SSL is ready go back to Webmail > Hit User on the Domain you wanna use > Now you can add Users, set Passwords, Storage and Names.

All Users set? Okay! Now we make sure you can use them.
Go to your AA-Panel Home-Page. > Enter the 1-Click-Deployment Addon > Choose Roundcube > Hit "One-Click" > As Domain enter "webmail.yourdomain.tld" > Now go to Website > Add an SSL Cert to the Website > Go to https://webmail.yourdomain.tld > Login with the Data you created before in the Webmail Addon.

Enjoy

(I am only a tutorial writer! If you have problems with the installation please write a post here in the forum, I can not help you with Problems. Thanks for your understanding.)