When you set up a sync filter on some CRM fields (flexible in SFDC, on MSD, it's handled with a standard SyncToMkto field. See Create a Custom Dynamics Sync Filter - Marketo Docs - Product Docs), if the filter is activated, the sync stops immediately (see "Sync with Marketo" mysteries part 1). The result is that Marketo does not know the sync has been stopped, excepted for a sync error message that is not usable in any filter / trigger.
This idea is that in this case, a last sync should occur, only for the sync filter field. This would enable Marketo to log a data value change and the Marketo user to set up smart campaigns accordingly (such as a smart campaign that deletes the lead from Marketo).
This last sync would only occur if the lead is still in Marketo, of course. If the lead is no longer there or has never been there, it should not trigger the creation of a lead in Marketo.
-Greg
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