About
Opens a short SMTP session to a public mail host to read the banner and STARTTLS support. It does not deliver mail.
How to use
Enter a host such as smtp.gmail.com and a port. The server opens a short TCP session and returns the result.
What this tool checks
Connectivity, SMTP banner, and whether STARTTLS can be negotiated. It answers whether the server is listening, not whether a password works.
How to read the results
Connecting and advertising STARTTLS is transport only. Auth failures, quotas, and blocklists belong in real sending logs.
Limits and safety
The probe starts from the CheckKit server, not your network. Do not repeatedly probe hosts you are not allowed to test.
FAQ
Does it send a test message?
No. It opens a short connection, reads the greeting, then disconnects.
Which port: 25, 465, or 587?
25 is often blocked by cloud providers; 587 is common for STARTTLS submission; 465 is often SMTPS. Use the port your provider documents.
What does a timeout usually mean?
A firewall dropped the port, the host is wrong, or the peer only allows certain IPs.
Related tools
- Email tools
- Gmail Address Check
Paste @gmail.com addresses (up to 10 per run).
- Outlook Authorized Mail Read
Format: email|refresh_token|client_id.
- Domain MX Record Lookup
View a domain’s mail exchanger records.
- Raw Email Header Parser
Paste raw headers to inspect routing and authentication fields.
- Public TCP Port Probe
Check whether a port is open on a public host.