Well it depends what setting you put in server manager
Try
https://Neo/webmailYou do need to enable webmail in the server manager and chose what type of access you allow http or https and whether local or public
As far as spammassassin is concerned it depends on whether you are using POP or IMAP.
You need to instal user manager and enable procmail for each user.
If IMAP then you should see the junkmail folder in your email client.
If you are using POP then do not tell spamassassin to send to the junkmail folder, the only way you will get to see the folder is by using webmail.
If you use POP then messages considered as spam will be delivered as usual, but you can tell spamassassin to apend the SPAM report to the message. That way it is pretty clear which messsages are spam and which messages are not.
You can set up a rule in procmail to handle these messages as you see fit.
Hope this helps
Ray