Email open is increasingly not a great signal for someone having engaged with your email due to privacy changes on many email clients (eg. Mail on IOS). But it's definitely a good idea to monitor opens, clicks, replies and use these signals for calculating lead scores and planning follow-ups. At Outfunnel we think it's best practice to sync email signals like opens, clicks and replies back to Pipedrive as Activities, so they can be filtered in the sales tools. (We currently do this for campaigns sent from Mailchimp and ActiveCampaign, with Sendinblue and Hubspot coming soon).