Knowing an email was sent is useful. Knowing whether the person opened it, clicked it or replied is what tells you who to follow up with.
Fuse writes that straight onto the contact record, so you can filter and build views on it in your CRM.
This is available on Attio today. HubSpot, Zoho and Pipedrive are coming soon, and Salesforce is behind them.
The fields Fuse creates
On Attio these are attributes on the Person object. Fuse creates them itself the first time engagement sync runs, so there is nothing to set up. They are named distinctly enough that they will not collide with your own attributes, and Fuse only ever writes to these three.
Availability
Salesforce is the hardest of the five. Its API does not allow creating custom fields the way the others do, and new fields there stay hidden until an administrator grants access to them per profile. Doing it properly needs a different approach.
The whole picture, not per campaign
These fields describe the person, not a single campaign. Someone in three campaigns gets one combined view: if they opened one and clicked another, they show both Opened and Clicked.
Fuse last engaged at and Fuse last campaign always refer to their most recent engagement across everything.
This is deliberate. Your CRM holds one record per person, and the question a salesperson asks is “has this person engaged?”, not “what did they do in campaign four?”. For per-campaign detail, use the campaign report in Fuse.
Always current
Unlike sent emails, these fields are kept up to date. When someone who had opened later clicks, their record is updated to show both. The fields always reflect where that person stands today.
What it needs
Engagement sync is on by default. It does need Push contact records enabled, under Settings → Integrations → your CRM on the Sync tab, because engagement is written onto contact records. With contact pushing off there is nothing to write it to and engagement sync stays idle.
A note on opens
Open tracking uses a tracking pixel, and some email clients, Gmail in particular, fetch that pixel automatically before a human has read anything. Opened is therefore a softer signal than the others.
Clicked and Replied are far stronger indicators of genuine interest. If you are building a follow-up list, prefer those.
Timing
Engagement sync runs about once an hour, so a click just now appears on the contact within the hour.
The first run backfills everyone who has engaged historically, which can take a few passes on a large account. 
