Deliverability testing | Detection.FYI

Reconnaissance: All recipients cc/bcc'd or undisclosed

Sep 23, 2026 · Attack surface reduction Deliverability testing ·
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Recon messages, a form of deliverability testing, are used to validate whether a recipient address is valid or not, potentially preceding an attack.

All recipients are bcc'd or undisclosed, with no links or attachments, and a short body and subject from an unknown sender.

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Reconnaissance: Large unknown recipient list

Sep 23, 2026 · Attack surface reduction Deliverability testing ·
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Recon messages, a form of deliverability testing, are used to validate whether a recipient address is valid or not, potentially preceding an attack.

There's a large number of recipients that are unknown to the organization, no links or attachments, and a short body and subject from an unknown sender.

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