Australian Information Security Manual ISM-1502: Emails arriving via an external connection where the email source address uses an internal

Emails arriving via an external connection where the email source address uses an internal domain, or internal subdomain, are blocked at the email gateway.

Maintained by Gerard BlokdykVerified against the published standard 31 May 2026Control text last updated 21 May 2026

Other controls in Guidelines for email

ISM-0264 An email usage policy is developed, implemented and maintained.
ISM-0267 Access to non-approved webmail services is blocked.
ISM-0269 Emails containing Australian Eyes Only, Australian Government Access Only or Releasable To
ISM-0270 Protective markings are applied to emails and reflect the highest sensitivity or classific
ISM-0271 Protective marking tools do not automatically insert protective markings into emails.
ISM-0272 Protective marking tools do not allow users to select protective markings that a system ha
ISM-0565 Email servers are configured to block, log and report emails with inappropriate protective
ISM-0567 Email servers only relay emails destined for or originating from their domains (including

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