UM outbound faxing requires MS Outlook (standard not Express or WebMail) and a fax card in the VPU. There is a client you must load into the MS Outlook client on the end users who want this function. OB faxing requires a Level 3 key if an older unit or a standard VPU license if purchased recently. Inbound faxes will work with any email client but still needs a fax card.