SMTP Test: Diagnose Why Your Email Won't Send

SMTP Test

An SMTP test verifies that your email sending configuration works, checking the server host, port, credentials, and TLS connection so you can diagnose why mail is failing to send.

What an SMTP test checks

It connects to your SMTP server and walks the conversation between client and server, confirming the host and port are right (usually 587 or 465), the username and password authenticate, and the TLS or SSL connection establishes. When mail is failing to send at all, rather than landing in spam, this is the test to run.

Common failures it catches

An authentication error usually means wrong credentials or, on Microsoft 365, SMTP AUTH disabled on the tenant. A connection timeout usually means a blocked port. A TLS handshake error means the encryption mode doesn't match the port. A 550 error points at the recipient or a content or reputation block rather than your configuration.

Beyond the SMTP test

A passing SMTP test means mail will send, not that it'll reach the inbox. For that, add a spam test email and confirm authentication. A lower-level option is a telnet smtp test run by hand.

How Nitrosend removes the SMTP guesswork

There's no host or port to test because you don't configure SMTP by hand. You connect an account from your AI agent and send, and once DNS setup is complete the Setup center sends a real test email automatically to confirm the path end to end.

FAQ

What is an SMTP test?

A check that your email server's host, port, credentials, and TLS settings are correct, used to diagnose why mail is failing to send rather than why it lands in spam.

Why is my SMTP test failing?

Common causes are wrong credentials, a blocked port, an encryption mode that doesn't match the port, or SMTP AUTH disabled on a Microsoft 365 tenant.

Does a passing SMTP test mean my email will reach the inbox?

No. It means the message will send. Inbox placement also depends on authentication, reputation, and content, which a spam test checks.