Watson report about to be sent for process id: 12800, with parameters: E12IIS, c-RTL-AMD64, 15.01.0466.037, w3wp#MSExchangeOWAAppPool, M.E.C.Owa2.Server, M.E.C.O.S.C.OwaMapiNotificationManager.SubscribeToSuiteNotification, System.NotSupportedException, 2c3e, 15.01.0466.037.

Log Name:      Application
Source:        MSExchange Common
Date:          26/06/2018 08:52:53
Event ID:      4999
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      %COMPUTERNAME%.domain.suffix
Description:
Watson report about to be sent for process id: 12800, with parameters: E12IIS, c-RTL-AMD64, 15.01.0466.037, w3wp#MSExchangeOWAAppPool, M.E.C.Owa2.Server, M.E.C.O.S.C.OwaMapiNotificationManager.SubscribeToSuiteNotification, System.NotSupportedException, 2c3e, 15.01.0466.037.
ErrorReportingEnabled: True

Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSExchange Common" />
    <EventID Qualifiers="16388">4999</EventID>
    <Level>2</Level>
    <Task>1</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2018-06-26T07:52:53.000000000Z" />
    <EventRecordID>7924947</EventRecordID>
    <Channel>Application</Channel>
    <Computer>%COMPUTERNAME%.domain.suffix</Computer>
    <Security />
  </System>
  <EventData>
    <Data>12800</Data>
    <Data>E12IIS</Data>
    <Data>c-RTL-AMD64</Data>
    <Data>15.01.0466.037</Data>
    <Data>w3wp#MSExchangeOWAAppPool</Data>
    <Data>M.E.C.Owa2.Server</Data>
    <Data>M.E.C.O.S.C.OwaMapiNotificationManager.SubscribeToSuiteNotification</Data>
    <Data>System.NotSupportedException</Data>
    <Data>2c3e</Data>
    <Data>15.01.0466.037</Data>
    <Data>True</Data>
    <Data>False</Data>
    <Data>w3wp#MSExchangeOWAAppPool</Data>
    <Data>
    </Data>
  </EventData>
</Event>

Anyone had any thoughts? Can’t find anything on Event ID: 2 for Exchange 2016

This appears to be an issue with mail flow rules and disclaimers - if you disable the rules and clear the bad mail queues and then reinstate the disclaimers/rules then everything seems to resolve itself.

Well that is what we did anyway....