Start/notes.ini Parameters/SMTPMaxConnections

SMTPMaxConnections

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Parameter: SMTPMaxConnections
Short description: Maximum number of simultaneous inbound SMTP connections – limits the load on the SMTP listener.

Profile

Parameter
SMTPMaxConnections
Category
Mail / Router
Component
Server
Available since
9.0.1
Supported versions
9.0.1, 10.0, 11.0, 12.0, 14.0, 14.5, 14.5.1
GUI equivalent
Configuration document
Possible values
Integer (typically 200–5000)

Description

SMTPMaxConnections defines how many inbound SMTP connections the Domino listener accepts simultaneously. The value protects against overload (e.g. during spam waves or misconfigured senders that open many connections). Once the limit is reached, the listener rejects new connections with a temporary error – reputable senders retry later, bad clients give up. The value should be chosen in relation to mail volume and SMTPMaxConnectionsPerIP (if used).

Example configuration

SMTPMaxConnections=2000

Notes & pitfalls

  • Values that are too low can lock out legitimate mail servers during load spikes – check SMTP logs for 421 Too many connections.
  • Takes effect after restarting the SMTP task.
  • Combines well with antispam pre-filtering and connect-time restrictions in the Configuration document.
  • For DDoS protection, additionally use a reverse proxy / edge gateway.