Hello,
regarding your issue with Horde.
when you try to log into horde.
you need the username and password.
I will explain with an example.
for instance , inside Plesk I have created a domain account : wserv.co.il
now , through Plesk I have created a new email box :
swsoft@wserv.co.il
when I will try to log into horde , I will need to use the following username and password :
username : swsoft
password : when you create a new email box through plesk then you also need to set a password , then you need to use that password.
regarding automatically log into horde , there no such feature.
regarding changing password for email box through horde.
it does't supported.
if you want to change a password for email box then you need to do it through Plesk control panel.
now, I suggest you to start reading the documentation of Plesk for windows platform ( I am not a worker from SWSOFT and I can say 100% that you didn't read the documentation ).