sublimelowRule

Sender: Local part built from recipient domain and mailbox

Flags inbound messages where the sender's local part is constructed by combining the recipient's domain name and mailbox name (e.g., domain_mailbox). This pattern is commonly used to make the sender address appear related to or originating from the recipient's own organization, helping the message blend in and evade scrutiny.

MITRE ATT&CK

T1566.002 T1534 T1656 T1566 T1566.001 T1598 T1036 T1027

initial-accessdefense-evasion

Detection Query

type.inbound
and sender.email.local_part == strings.concat(recipients.to[0].email.domain.sld,
                                              '_',
                                              recipients.to[0].email.local_part
)
and sender.email.domain.root_domain != recipients.to[0].email.domain.root_domain

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Tags

Attack surface reduction

Raw Content

name: "Sender: Local part built from recipient domain and mailbox"
description: "Flags inbound messages where the sender's local part is constructed by combining the recipient's domain name and mailbox name (e.g., domain_mailbox). This pattern is commonly used to make the sender address appear related to or originating from the recipient's own organization, helping the message blend in and evade scrutiny."
type: "rule"
severity: "low"
source: |
  type.inbound
  and sender.email.local_part == strings.concat(recipients.to[0].email.domain.sld,
                                                '_',
                                                recipients.to[0].email.local_part
  )
  and sender.email.domain.root_domain != recipients.to[0].email.domain.root_domain
tags:
  - "Attack surface reduction"
attack_types:
  - "BEC/Fraud"
  - "Credential Phishing"
tactics_and_techniques:
  - "Spoofing"
  - "Evasion"
  - "Impersonation: Employee"
detection_methods:
  - "Header analysis"
  - "Sender analysis"
id: "fce2ba42-17a2-5b84-8760-0a5e641f0bb8"