Clients are those contacts and companies you do marketing work for. A client can be an external organization or an internal contact in another department.
As an example, an advertising agency implementing MDM will have many clients. Their clients are the companies that hire them to put together marketing campaigns. As a second example, the marketing department of a manufacturing company makes a business decision to store any employee that requests work, but who is external to the marketing department, as a client. Even though they don’t charge for the work they do, they chose to separate external work requestors from their Staff users. Other organizations choose to keep both staff and internal clients in the same list and remove access to the client functionality with user permissions.
Vendors do work for you or they are the people and organizations that you buy services from. External printers, caterers, media companies, and contractors are examples of vendors commonly used by marketers.
All users created in Office 365 are added to MDM as a Staff contact. Staff typically are comprised of users and of other contacts internal or external to the marketing department who do not require a license. Find Staff in the Settings area.
The majority of most MDM contacts, Marketing contacts and companies are those the marketing department markets to. Typically they are added to campaigns and segmented with marketing lists based on a variety of attributes. Marketing contacts are not available for use with all functions. For example, a marketing contact cannot be specified as the “From” contact when sending an email marketing message.