According to the IBM Lotus Domino Administrator Help, the Domino SNMP Agent must be installed on the Domino server.

The agent consists of:

• LNSNMP
• QuerySet Handler
• Event Interceptor

The MIB file is located at the Domino executable directory of any Domino 7 server or newer.

A copy is here: NOTES-MIB. But may not be up to date.

Objects with the string --<< , contains Domino statistics.

Example:

lnDeadMail OBJECT-TYPE --<< INT mail.dead
   SYNTAX INTEGER (0..2147483647)
   ACCESS read-only
   STATUS optional
   DESCRIPTION
     "Number of dead (undeliverable) mail messages."
   ::= { lnMail 1 }

lnTotalMailFailures OBJECT-TYPE --<< INT mail.totalfailures
   SYNTAX INTEGER (0..2147483647)
   ACCESS read-only
   STATUS optional
   DESCRIPTION
     "Total number of routing failures since the server started."
   ::= { lnMail 3 }

lnMailTransferFailures OBJECT-TYPE --<< INT mail.transferfailures
   SYNTAX INTEGER (0..2147483647)
   ACCESS read-only
   STATUS optional
   DESCRIPTION
     "Number of mail messages the router was unable to transfer."
   ::= { lnMail 19 }

The MIB file contains traps which may be useful. See Monitoring with SNMP traps.

Interesting traps:

lnServerDownTrap TRAP-TYPE
   ENTERPRISE notes
   VARIABLES { lnEvtServer }
   DESCRIPTION
     "This trap indicates that the Notes server has gone down."
   ::= 12

lnServerPulseFailedTrap TRAP-TYPE
   ENTERPRISE notes
   VARIABLES { lnEvtServer }
   DESCRIPTION
     "This trap indicates that the Notes server is not responding
      to the Lotus Notes SNMP agent.  The server may have crashed,
      or may be busy."
   ::= 13

lnServerNotRespondingTrap TRAP-TYPE
   ENTERPRISE notes
   VARIABLES { lnEvtServer }
   DESCRIPTION
     "This trap indicates that the Notes server has not responded
      to the Lotus Notes SNMP agent for several minutes.  There is
      a chance that the Notes server may have crashed."
   ::= 16