"Authentication failed " can't acess to snappymail

hello i installed CyberPanel on my ubuntu 18.04 vps and i created my website with wordpress
and i need to create some emails with my domain name
i created one but can’t acess to snappymail to test it
all i got is" Authentication failed "
ive tried the solution proposed here Workaround for (some) Problems: Can´t login in Rainloop
but still dosen’t work

First ubuntu 18.04 why?
then check the checktls results

i didn’t understand what you mean ??

Please have a look into the original post.
I posted the missing thing