Change Password from Mail account


I installed Virtualmin GPL, because I wanted to test it first times. Now I furnished a virtual server and put on several Mail accounts.
But how a user can change the password now?


Have the user log into "Usermin" to change his own password. https://domainname.tld:20000

Ok, thank you.
I already imagined. I have only the problem that "user min" cannot be opened, if IPTables are active. The haven is approved, also different haven tried.