Start/notes.ini Parameters/SMTPRelayHostsAndDomains

SMTPRelayHostsAndDomains

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Parameter: SMTPRelayHostsAndDomains
Short description: Whitelist of hosts / domains that are allowed to use the Domino server for SMTP relay – decisive for protection against open relay.

Profile

Parameter
SMTPRelayHostsAndDomains
Category
Mail / Router
Component
Server
Available since
9.0
Supported versions
9.0.1, 10.0, 11.0, 12.0, 14.0, 14.5, 14.5.1
GUI equivalent
Configuration document
Possible values
Comma-separated list, e.g. *.example.com,partner.de,10.0.0.0/8

Description

The Domino SMTP listener only accepts mail to external recipients for forwarding (relay) if the submitting host is on the relay whitelist. SMTPRelayHostsAndDomains holds this list – either as wildcards (*.example.com), individual hosts, or network ranges. Without an entry the server (together with the default protection rules) behaves as a closed relay and accepts relay only for locally authenticated senders, which is mandatory for internet operation. Misconfigured wildcards (e.g. *.com) turn the server into an open relay – which leads immediately to spam abuse and blacklisting.

Example configuration

SMTPRelayHostsAndDomains=*.acme.local,10.10.0.0/16

Notes & pitfalls

  • Never enter * alone – that is open relay.
  • Works together with other relay restrictions in the Configuration document; on conflicts notes.ini wins.
  • Takes effect after restarting the SMTP task.
  • Regularly test open-relay status externally (e.g. with mail-tester.com or MXToolbox).