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Low Severity

Reconnaissance: Empty message from uncommon sender

Description

Detects incoming messages that are completely empty, containing no subject line, message body content, or file attachments. Such messages may be used for reconnaissance, delivery confirmation, or as part of multi-stage attacks.

References

No references.

Sublime Security
Created Feb 25th, 2026 • Last updated Feb 25th, 2026
Source
type.inbound
and subject.base == ""
and (
  body.plain.raw is null
  or body.plain.raw == ""
  or regex.imatch(body.plain.raw, '^\s*$')
)
and (
  body.html.raw is null
  or body.html.raw == ""
  or regex.imatch(body.html.raw, '^\s*$')
)
and length(attachments) == 0
and profile.by_sender().prevalence != "common"
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