Hey, we are moving out of an old email marketing platform into Marketo. Our contacts database has over 1 million contacts in it, but we will only have space for half of that in Marketo. Before syncing CRM to Marketo, I believe I need to mark some of our contacts as "do not sync to marketo". I am attempting to use data from our old marketing platform to identify those for "do not sync..."
We are a non-profit association, and I am initially considering saying "if you have not opened an email from us in 1 year then i will not sync you". That seems like a long time period, but no previous contact cleaning has been done.
Is there a best practice/standard for how long someone can be disengaged before removing from your list?