The SMTPTester Blog
Practical, no-fluff guides on SMTP, authentication, encryption and email deliverability. Written by engineers who debug this stuff for a living.
Troubleshooting
How to Fix SMTP Authentication Errors (535, 530, 534)
A practical, copy-paste friendly guide to debugging SMTP authentication failures across Gmail, Microsoft 365, SendGrid, and self-hosted servers.
Sep 12, 2025 9 min read
Read article Best Practices
Best SMTP Settings for Reliable Email Delivery in 2025
The exact ports, encryption modes, authentication, and timeouts to use for production SMTP — plus a copy-paste config for the top providers.
Oct 4, 2025 8 min read
Read article Architecture
SMTP vs API Email Sending: Which One Should You Use?
A pragmatic comparison of SMTP relay and HTTP API based email sending — performance, observability, deliverability, and when to pick each.
Oct 21, 2025 7 min read
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