A Request for Information asks specific questions about the services an email marketing vendor provides. It is usually a relatively short document and is used when no final decisions for direction have been made. An RFI is often used together with a Request for Proposal (RFP) and a Request for Quotation (RFQ), sometimes these documents are combined.
The RFI is often used as a pre-qualifier to determine which vendors will receive an RFP or RFQ. Eliminating many from a bigger set of possible vendors (long list) to create a smaller set of suitable vendors (short list). The client probably doesn’t have their problem crystallized or well defined and is looking for someone to help them identify the problem. Usually when a winning RFI, the Email service provider may be the favored vendor to compete for a RFP.