People with virtual mailboxes may use the normal services for accessing their email, such as SSL IMAP and POP, and https://webmail.hcoop.net.They authenticate giving their full e-mail addresses as usernames, in contrast to the situation for normal UNIX users.
Note: If you try to log in to the web interface this will fail because the mail directory has not been initialized yet. Send a test message to the new account, then verify that the $MAILDIR directory now has some files (not only directories!) using find $MAILDIR -type f, and then try to access the account from the web interface.