SMTP Banner Probe
Connect to a Simple Mail Transfer Protocol (SMTP) server, capture its banner + EHLO capabilities, and test STARTTLS.
Email down = revenue down. Know before your customers do.
Monitor your mail server 24/7
- ✓SMTP / POP3 / IMAP monitoring
- ✓Port connectivity checks
- ✓Response time tracking
- ✓Email + Slack + SMS alerts
- ✓Incident history
- ✓Status page integration
Frequently Asked Questions
What does the SMTP Banner Probe check?
It connects to a Simple Mail Transfer Protocol (SMTP) server on port 25 or 587, reads the greeting banner, sends an EHLO command to list the server's capabilities, and tests whether STARTTLS is available and negotiates successfully. Results show the full banner, EHLO extensions (AUTH methods, size limits, etc.), and Transport Layer Security (TLS) negotiation status.
What is STARTTLS and why is it important?
STARTTLS upgrades a plain-text Simple Mail Transfer Protocol (SMTP) connection to an encrypted Transport Layer Security (TLS) connection before any credentials or message content are transmitted. Without it, email between servers can be intercepted in transit. Most modern mail servers require STARTTLS; its absence is a serious security issue and may fail compliance audits.
What does the EHLO response tell me?
EHLO lists the Simple Mail Transfer Protocol (SMTP) extensions the server supports: STARTTLS (Transport Layer Security (TLS) upgrade), AUTH LOGIN PLAIN (authentication methods), SIZE (max message size), 8BITMIME (8-bit content), SMTPUTF8 (international addresses). These affect how clients and other mail servers should connect and authenticate.
Why can't I probe port 25 from my own network?
Most Internet Service Providers (ISPs) and cloud providers block outbound port 25 to prevent spam. This tool probes from our infrastructure where port 25 is open. For testing user submission, try port 587 (SUBMISSION with STARTTLS) or 465 (Simple Mail Transfer Protocol Secure (SMTPS) with implicit Transport Layer Security (TLS)), which are typically open.