SMTP Connectivity TestUnder Development
Test whether an SMTP mail server is reachable, with greeting, EHLO capabilities, and STARTTLS verification.
Tests reachability, greeting, and TLS capabilities from PacketFlo servers. Never sends mail or tests authentication.
Enter a mail server to test connectivity
Checks TCP latency, SMTP 220 banner, EHLO capabilities, and STARTTLS/SMTPS handshake.
SMTP Connectivity Test checks whether an email server is reachable from PacketFlo's server-side infrastructure and responds correctly to an SMTP connection. It verifies DNS resolution, measures TCP connection latency to the chosen port (25, 465, 587, or 2525), captures the initial SMTP 220 greeting, sends EHLO to inspect advertised capabilities, and validates TLS handshakes via STARTTLS or implicit TLS.
This tool is strictly a passive diagnostic probe. It does not authenticate, does not send email, and does not test mailbox delivery or relay. It answers whether network firewalls, port blocks, or TLS certificate mismatches prevent mail servers or clients from connecting to the service.
For inbound email routing configuration, see MX Lookup. To verify sender authentication policies, use SPF Checker, DKIM Checker, and DMARC Checker. To test all mail authentication in one pass, use Mail Health Check.
| Port | Protocol & Common Usage |
|---|---|
| 25 | Standard SMTP server-to-server mail relay. Uses Plain SMTP with optional opportunistic STARTTLS. |
| 587 | SMTP Submission port for mail clients (MUAs) submitting outgoing mail. Commonly requires STARTTLS. |
| 465 | SMTPS / Implicit TLS. Directly establishes a TLS handshake before reading the SMTP greeting banner. |
| 2525 | Common alternate submission port used when ISPs or cloud providers block outbound port 25. |
Frequently asked questions
Does this tool test if my email will be delivered?
No. This tool tests whether the mail server is reachable on a specific port and responds correctly to an SMTP connection. It does not attempt authentication, compose messages, or test mailbox delivery.
What is the difference between port 25, 587, and 465?
Port 25 is used for inter-server mail transfer. Port 587 is the standard submission port used by mail clients, typically requiring STARTTLS. Port 465 connects using implicit TLS (encryption begins immediately before SMTP commands).
Why is STARTTLS important?
STARTTLS allows opportunistic encryption on standard plain-text SMTP ports (25, 587, 2525). It protects in-transit communications against passive eavesdropping and interception.