- Distribution list -- any e-mails sent to the address will be forwarded to people on the list (into their personal inboxes)
- Shared Mailboxes -- emails sent to the address will appear in a shared folder, visible to anyone in the organisation who has permission
These options do not require an additional user license for Office 365.
In some situations (if you need to do complex mail handling, or use more advanced Office 365 features on the address) you may need to purchase an additional user license.
These cases are not common, but should be factored in when quoting if the customer is likely to need more than simple inbound mail receiving and sending on the address.