Link analysis
Stoïk Email Security inspects the links found in the emails it analyzes. This page explains what our systems do with those links, and how to report a link that should be left alone.
Why links are resolved
Phishing rarely gives itself away in the body of a message. The signal is in the destination: a shortened link that lands on a lookalike domain, or a redirect chain that ends on a domain registered three days ago.
Reading a link as it is written tells us none of that. The link has to be resolved to see where it actually goes.
What the analysis does
For each link in an analyzed email, Stoïk sends one HTTP HEAD request and follows up to five redirects.
A HEAD request asks a server for the response headers only. It is the same request as opening the page, minus the page content. It is used instead of a full page load because it is the lightest way to learn where a link leads.
From it, Stoïk records the end of the redirect chain, the number of hops, and the reputation of the destination domain. The request times out after two seconds.
When the analysis goes further
If the destination domain looks suspicious, meaning it has a poor reputation, was registered recently, or is rarely seen across the mailboxes we protect, the page is opened in an isolated browser environment and a screenshot is captured. A vision model then judges whether the page is a credential harvesting kit, and which brand it imitates.
A domain that is well established and commonly seen never reaches that stage. A link to a major provider is resolved, but its page is never loaded.
Loading a page means the page runs its own JavaScript, exactly as it would in a visitor's browser, and a page can issue requests of its own while it does. Those requests come from the page, not from instructions we give it. When a page is unreachable because of an anti-bot challenge, the capture goes through a solver that negotiates the challenge first.
What the analysis never does
Stoïk does not act on your behalf. Our analysis clicks no button, fills in no form, and never uses your credentials. Where a link would trigger something by the mere fact of being requested, it is not requested at all: see Links that are skipped entirely.
Exception: file-sharing platforms
Attackers run a growing share of their phishing through legitimate file-sharing services. A document shared from a well-known platform borrows that platform's reputation and gets past most filters, while the trap sits inside the shared file. Judging that email means reading what was actually shared.
These platforms do not hand a shared document to a plain page load. Reaching one means making the request the platform defines for it: a query to its own API, or the anonymous authentication step a share link performs using the key already contained in the link.
Stoïk does this only on the platforms it explicitly supports, and only with what the link already carries.
Links that are skipped entirely
Some links change something the moment they are requested, even by a HEAD. An electronic signature link can mark a document as viewed or consume a one-time token. A quarantine digest link can release a blocked email. A one-click unsubscribe link takes the recipient off a mailing list, and a calendar invitation link can record an RSVP.
The HTTP standard is explicit here. RFC 9110 section 9.2.1 defines GET and HEAD as safe methods: a client sending one neither requests nor expects any change of state on the server. The same section adds that when a parameter in the URL selects an action, the owner of that resource must disable the action when it is reached with a safe method. The rule exists so that automated retrieval can work without causing harm.
Not every service follows it.
Reporting a link
If you see an action on one of your services that you believe came from our analysis, report it to Stoïk through your usual support channel.
Useful details:
The service concerned
The address of the mailbox affected
Roughly when it happened
The link itself, if you still have it
The destination is added to the allowlist, and you are notified once the change is live.
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