The numbers for the email sunsetting feature.
14 unopened emails - Daily to Weekly
16 unopened emails - Weekly to Monthly
22 unopened emails - Monthly to Never
These numbers work consecutively. I.E. it does not go, 14 unopened daily emails are followed by 16 unopened weekly emails. It goes 14 unopened daily emails, followed by two unopened weekly emails for a total of 16 and then it gets switched to monthly.
If the lead opens up any of these emails it will automatically switch them back to daily and the counter restarts.
Additionally, a lead can manually change the settings for themselves to turn property update emails on.