FaxMail merge is a service by Popfax.com that allows users to send personalized faxes to multiple recipients at once. It works by merging placeholders in a master fax document with recipient information from an Excel spreadsheet. The user creates the master fax, adds merge fields, and uploads both files to Popfax via email. Popfax then merges the documents and sends individualized faxes to each recipient at the standard per-minute rate.