Only the domain is sent to hin.ch.

What the HIN check looks up

HIN's domain directory
HIN maintains a directory of mail domains connected to the HIN platform, for example through the HIN mail gateway of a practice, hospital or insurer. Messages between connected domains travel encrypted via HIN. The check queries exactly this directory.
Why only the domain matters
HIN decides per domain, not per mailbox. The tool therefore strips the part before the @ in your browser and sends only the domain. A single address can neither be confirmed nor ruled out this way.
Subdomains count separately
Matching is exact. If insel.ch is connected, that does not automatically apply to spital.insel.ch. Organisations using subdomains for mail have to register each one with HIN.
What “not reachable” means
Messages to this domain are not automatically protected by HIN. Whether they arrive encrypted then depends on the sender's mail system, for example TLS or its own encryption gateway.

Data source: domain checker of Health Info Net AG (HIN). Unofficial tool without warranty; authoritative is the check on hin.ch. HIN basics

Feedback

Is this tool useful to you? Is a feature missing, or is a result wrong? Feedback right here in the comments is welcome.

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