How to calculate email OPENS

[RFalcone]

We are currently pulling all email events from the API

with the /marketing-emails/v1/  endpoint.

With that we have all email events and it works well.

However, since we are retrieving all events we have all OPEN events and when calculating OPENs we have a much higher OPEN rate than what HubSpot calculates.

We are trying to determine which OPEN emails should be filtered so we can match what HubSpot deems as a valid OPEN.

I do not see any field that shows what is a reliable OPEN.

Is there a field that can used to determine what emails HubSpot is using in it's calculation of email OPENs?

Can UserAgents be used to determine this as well as what platform was used to open the email?

I see that HubSpot recently filtered out Apple.

Any help appreciated.