Transactional & SMTP
SMTP Error Codes Explained (and How to Fix Them)
A practical reference for SMTP error codes: how to read a reply in ten seconds, the difference between 4xx soft bounces and 5xx hard bounces, lookup tables for the codes you will actually hit, and fixes for the five that cause most real-world pain — plus the ports that quietly cause silent failures.
Aug 16, 20269 min read