Once you have created a mailbox in Plesk e.g. sales@yourdomainname.co.uk, you can create email aliases in Plesk for the mailbox e.g. billing@yourdomainname.co.uk so that any mail sent to one of the email aliases will be delivered to the mailbox.
Please follow the link below for a tutorial:
How to create an email alias in Plesk
For further support and assistance on setting up your email review the following tutorials:
How to create an email redirect in Plesk
How to create a POP email account (mailbox) in Plesk
Setup your email using Microsoft Outlook Express (mail client)
How to setup a POP account in Microsoft Outlook
If you have any problems with setting up your email services please let us know.