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About SMTP Tester Online
This tool connects to your SMTP server using the credentials you provide and attempts to send a test email. It tells you whether the connection succeeds, whether authentication passes, and whether the message is accepted for delivery.
SMTP testing is essential when configuring email sending for a new application, debugging "my server can't send mail" complaints, validating credentials before deploying production code, or troubleshooting deliverability problems with a specific recipient.
Use a sandbox or dedicated test recipient when running tests. Sensitive credentials are sent over TLS where supported; never use the tool on a server you don't own or have explicit permission to test.
How to use this tool
How to test an SMTP server's greeting
Enter the SMTP host
Type the SMTP host (e.g. mail.example.com) into the "SMTP host" field. Up to 253 characters. Private IPs are rejected.
Pick the port
Port defaults to 25 (the relay port). Common alternatives: 587 (submission with STARTTLS), 465 (implicit TLS / SMTPS). The probe is plain-text TCP, no TLS upgrade.
Press Run
Our server opens a TCP connection, waits for the SMTP banner, sends EHLO toolsina.com, and captures the multi-line response. The session is closed after ~4 seconds.
Read the transcript
Output is a transcript array — server greeting plus capability lines (250-PIPELINING, 250-SIZE, 250-STARTTLS, 250-AUTH, etc.). Missing STARTTLS means the host won't upgrade to TLS on this port; missing AUTH usually means no authenticated relay.