Start/notes.ini Parameters/SMTPMaxForRecipients

SMTPMaxForRecipients

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Parameter: SMTPMaxForRecipients
Short description: Maximum number of recipients per inbound SMTP message (protection against mail bombing / spam).

Profile

Parameter
SMTPMaxForRecipients
Category
Mail / Router
Component
Server
Available since
R6
Supported versions
9.0.1, 10.0, 11.0, 12.0, 14.0, 14.5
GUI equivalent
Configuration document (Router/SMTP → Restrictions and Controls)
Possible values
Integer, e.g. 100 (0 = unlimited)

Description

SMTPMaxForRecipients limits how many RCPT TO recipients the Domino SMTP listener accepts per inbound message. Once the limit is exceeded, Domino rejects further recipients with a 5xx code.
It is an important protective measure against mail bombing and accidental mass-send loops from internal applications. Recommended values for mid-sized organizations are 50–500.

Example configuration

SMTPMaxForRecipients=100

Notes & pitfalls

  • The Configuration document entry overrides this notes.ini setting.
  • Test the impact on internal newsletter mailings.
  • Values that are too low cause 5xx errors for legitimate distribution lists.
  • Combines with SMTPMaxNumberOfRecipients (older synonym) and inbound connection limits.
  • The change only takes effect after restarting the SMTP listener.