Extended Simple Mail Transfer Protocol; an extension of SMTP that provides additional features for email transmission.
Modern technical acronym from 'Extended Simple Mail Transfer Protocol.' SMTP was developed in the early 1980s, with ESMTP extensions added in the 1990s to enhance functionality.
ESMTP exemplifies how internet protocols evolve—rather than replacing SMTP entirely, engineers added 'extensions' that maintain backward compatibility while enabling new features like authentication and encryption.
Complete word intelligence in one call. Free tier — 50 lookups/day.