SMTP Test
Test SMTP connectivity and verify that your email server accepts outgoing messages.
SMTP Configuration
Learn more & FAQ
What does the SMTP test tool do?
Before an application or mail client can send email, it has to establish a working SMTP connection to the mail server - the right host, port, encryption mode, and credentials. This tool connects to your mail server the same way your application would and reports exactly where in that process things succeed or fail.
How to read your results
Connection confirms the server is reachable on the port you tested. Delivery and Latency show whether a test message could actually be handed off and how long the round trip took. If the connection step fails, the issue is network or port-level (often a blocked port); if authentication fails after a successful connection, the issue is almost always credentials.
Frequently asked questions
Which SMTP ports should I test?
Port 587 (STARTTLS) is the standard for authenticated mail submission today, 465 (implicit TLS) is still widely supported, and port 25 is mostly used for server-to-server relay rather than sending from an application - many ISPs and cloud providers block outbound port 25 entirely to curb spam.
Why can't I connect to my mail server on port 25?
Many residential ISPs and cloud providers (AWS, Azure, GCP) block outbound connections on port 25 by default specifically to prevent compromised machines from sending spam directly. Use 587 or 465 instead, or request port 25 unblocked from your cloud provider if you specifically need server-to-server relay.
What's the difference between STARTTLS and implicit TLS?
STARTTLS (typically port 587) starts the connection unencrypted and upgrades to TLS partway through the handshake. Implicit TLS (typically port 465) encrypts the connection from the very first byte. Both are secure when working correctly; STARTTLS has historically had more implementation edge cases.
My connection succeeds but authentication fails - what's wrong?
A successful connection just confirms the server is reachable on that port. An authentication failure afterward usually means an incorrect username/password, an app-specific password requirement (common with Gmail/Microsoft 365), or an IP-based restriction on the mail account itself.
Does a successful SMTP test guarantee my emails will be delivered?
It confirms the connection and authentication work, which is a necessary first step, but delivery also depends on your SPF/DKIM/DMARC setup and sender reputation - the Email Security Check tool below covers that part.