Is there a bulk way to add a property through Hubspot API?
It is possible to add emails at once to Hubspot through the Import2 Wizard connection from the CSV file.
The steps to import Email from CSV into activity feed in Hubspot are pretty quick:
Upload your CSV file, select Email as the type of data to import
Map the fields you want on the Email itself (i.e. body of the email, timestamp) and the links to the records you want to associate the email to (i.e. contact, company, deal). You can use contact email for example to find the existing contact in HubSpot to link it to (you don’t have to use email, you can use any field on the contact, even custom ones)
Start the import
Please see here for more details on how to map fields importing into Hubspot.
Here the quick video overview of the steps described above: