Bitelio
§ T-15  —  Tool← All tools

Test any
SMTP server

Open a connection to any mail server and see how it responds — connect time, greeting banner, TLS support and the full EHLO capability list, in seconds.

SMTP connection test

Enter the hostname without a protocol, e.g. smtp.gmail.com

Submission / STARTTLS

This tool only tests connectivity, TLS and EHLO capabilities. It never logs in, sends email, or asks for your credentials.

§ 01Why test

Catch mail problems before your users do.

A silent SMTP server is a silent outage — verify it answers, encrypts, and advertises what you expect.

Confirm connectivity

Verify the server is reachable on the port you expect and measure how quickly it accepts a connection.

Check TLS support

See whether the server negotiates encryption — implicit TLS on 465 or STARTTLS on 25/587 — and which protocol it uses.

Inspect EHLO capabilities

Read the full list of extensions the server advertises, from SIZE and PIPELINING to AUTH and 8BITMIME.

Diagnose firewalls

A connection timeout or refusal usually means a firewall or the wrong port — surface it here, not in a stuck queue.

No credentials needed

The test only opens a connection and reads the handshake. It never authenticates, so you never share a password.

Instant results

Point it at a host and port and get the greeting, capability list and TLS status back in a single request.

§ 02SMTP explained

SMTP ports, demystified.

Which port to use — and how encryption actually gets negotiated on each one.

Port 587 — Submission

The modern default for sending authenticated mail. It starts unencrypted and upgrades to TLS via the STARTTLS command. Use this unless you have a reason not to.

Port 465 — Implicit TLS

The connection is encrypted from the very first byte (SMTPS), with no plaintext phase. Reinstated by RFC 8314 as a recommended submission port.

Port 25 — Relay

The original server-to-server relay port. Most residential and cloud networks block outbound 25, so it is rarely used for application sending.

Port 2525 — Alternate

Not an official standard, but widely offered as a fallback when 587 is blocked by a network. Behaves like 587 with STARTTLS.

STARTTLS vs implicit TLS

STARTTLS (25, 587) opens in plaintext and asks to upgrade. Implicit TLS (465) is encrypted from the start. This tool reports which model a server offers.

What EHLO tells you

After connecting, a client sends EHLO and the server replies with the extensions it supports — STARTTLS, AUTH, SIZE, PIPELINING and more. That list is what this tool reads back.

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Start with BitelioManaged SMTP relay

Frequently asked questions

Does this tool send email or log in to my server?

No. It only opens a connection, reads the greeting banner, and runs EHLO to list the server's capabilities and TLS support. It never authenticates, never sends a message, and never asks for a username or password. It is a pure connectivity and handshake check.

What is the difference between STARTTLS and implicit TLS?

Implicit TLS (typically port 465) encrypts the connection from the very first byte — the whole session is TLS. STARTTLS (typically ports 25 and 587) begins as a plaintext connection and then issues the STARTTLS command to upgrade to encryption mid-session. Both end up encrypted; they just negotiate it differently. This tool shows whether STARTTLS is advertised and, when the connection is already encrypted, the TLS protocol in use.

Which SMTP port should I use?

For sending authenticated mail from an application, use port 587 (submission with STARTTLS) as the default, or 465 for implicit TLS. Port 25 is the server-to-server relay port and is blocked on most networks for outbound application traffic. Port 2525 is a common unofficial fallback when 587 is blocked.

Why does the test time out or get refused?

A timeout usually means a firewall is silently dropping the connection, or nothing is listening on that host and port. A refusal means the host is reachable but actively rejected the connection on that port — often the wrong port for that server. Try a different port, or check that outbound traffic to it is allowed on your network.

What do the EHLO capabilities mean?

When a client connects, it sends EHLO and the server responds with the SMTP extensions it supports. Common ones include STARTTLS (can upgrade to TLS), AUTH (accepts authentication), SIZE (maximum message size), PIPELINING and 8BITMIME. Reading this list tells you what a server is capable of before you configure a client against it.